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1

Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides  

NASA Technical Reports Server (NTRS)

A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

Collins, J.; Rosner, D. E.; Castillo, J.

1992-01-01

2

THE NUCLEATION AND GROWTH OF GAS BUBBLES IN A NEWTONIAN FLUID: AN ENERGETIC VARIATIONAL PHASE FIELD APPROACH  

Microsoft Academic Search

In this paper, we study the nucleation and growth of gas bubbles in a Newtonian fluid. We employ a general energetic variational formulation with a phase-field method, and compare the analytical and numerical predictions of this new formulation with those of classical models. The new approach allows the study of bubble nucleation, growth and coalescence in a unified framework, and

AARON NABER; CHUN LIU; JAMES J. FENG

3

Nucleated growth patterns in binary phase-separating liquid gas systems  

NASA Astrophysics Data System (ADS)

We construct a model to simulate systems that have gas in coexistence with a binary liquid. We present a statistical mechanical approach similar to that used to derive the Van der Waals equation of state. However, in this case, we introduce two species of particle with different interactions between similar and dissimilar types, and from this we derive the Landau free energy density. In equilibrium, the system minimizes this free energy, and this allows us to construct the phase diagram. Using a binary lattice Boltzmann algorithm, we numerically model this system. In particular, we focus on the discovery of intriguing tentacle structures observed in a small area within the nucleation region. We show how these structures grow in time, and how this evolution is changed in the inertial, viscous and diffusive limits.

Pooley, Christopher; Yeomans, Julia

2005-03-01

4

Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania  

NASA Technical Reports Server (NTRS)

We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

1994-01-01

5

Dependence of particle nucleation and growth on high-molecular-weight gas-phase products during ozonolysis of ?-pinene  

NASA Astrophysics Data System (ADS)

We report the first time-dependent measurements of high-molecular-weight (up to 700 amu) gas-phase oxidation products from ?-pinene ozonolysis in an aerosol chamber under dry and low-NOx conditions. Measurements of products having mole fractions ranging from 10-14 to 10-11 were carried out with a chemical ionization mass spectrometer (the Cluster CIMS). Most products that were correlated with number concentrations of the smallest particles measured (10-20 nm) had molecular weights in the 430-560 amu range. Those products are proposed to be likely responsible for the initial nuclei formation and the early growth of the freshly nucleated particles based on their high molecular weights and chemical identities, both of which suggest low-volatility compounds. Another group of oxidation products in the lower mass range of 140-380 amu was well correlated with particles larger than 20 nm. We postulate that those products contributed to the later growth of particles (i.e., larger than 20 nm in diameter). Although particle nucleation in this study was primarily due to condensation of oxidation products from ?-pinene ozonolysis, the involvement of residual sulfuric acid vapor in particle nucleation cannot be totally excluded.

Zhao, J.; Ortega, J.; Chen, M.; McMurry, P. H.; Smith, J. N.

2013-08-01

6

Dependence of particle nucleation and growth on high molecular weight gas phase products during ozonolysis of ?-pinene  

NASA Astrophysics Data System (ADS)

We report the first time-dependent measurements of high molecular weight (up to 700 amu) gas-phase oxidation products from ?-pinene ozonolysis in an aerosol chamber under dry and low NOx conditions. Measurements of products having mole fractions ranging from 10-14 to -11 were carried out with a chemical ionization mass spectrometer (the Cluster CIMS). Most products that were correlated with number concentrations of the smallest particles measured (10-20 nm) had molecular weights in the 430-560 amu range. Those products are proposed to be likely responsible for the initial nuclei formation and the early growth of the freshly-nucleated particles based on their high molecular weights and chemical identities, both of which suggest low volatility compounds. Another group of oxidation products in the lower mass range of 140-380 amu was well correlated with particles larger than 20 nm. We postulate that those products contributed to the later growth of particles (i.e. larger than 20 nm in diameter). Although particle nucleation in this study was primarily due to condensation of oxidation products from ?-pinene ozonolysis, the involvement of residual sulfuric acid vapor in particle nucleation cannot be totally excluded.

Zhao, J.; Ortega, J.; Chen, M.; McMurry, P. H.; Smith, J. N.

2013-04-01

7

Bubble nucleation from gas cavities — a review  

Microsoft Academic Search

This review is concerned with the nucleation of bubbles in solutions supersaturated with a gas, in particular the bubble nucleation that occurs at specific sites, as a cycle. A classification system for the kinds of nucleation that occur is defined and discussed in order to place this specific form of nucleation into a better defined context. It is noted that

S. F. Jones; G. M. Evans; K. P. Galvin

1999-01-01

8

Properties of the seismic nucleation phase  

USGS Publications Warehouse

Near-source observations show that earthquakes begin abruptly at the P-wave arrival, but that this beginning is weak, with a low moment rate relative to the rest of the main shock. We term this initial phase of low moment rate the seismic nucleation phase. We have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1.1-8.1. The size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake, suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake. The seismic nucleation phase is characteristically followed by quadratic growth in the moment rate, consistent with self-similar rupture at constant stress drop. In this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it.

Beroza, G. C.; Ellsworth, W. L.

1996-01-01

9

Analysis of urban gas phase ammonia measurements from the 2002 Atlanta Aerosol Nucleation and Real-Time Characterization Experiment (ANARChE)  

Microsoft Academic Search

Gas phase ammonia (NH3) measurements were made in July and August 2002 during the Atlanta Aerosol Nucleation and Real-Time Characterization Experiment with two different chemical ionization mass spectrometry techniques. Correlations between the 1 min data from both instruments yielded a slope of 1.17 and an intercept of -0.295 ppbv, with a linear correlation coefficient (r2) of 0.71. Ambient NH3 mixing

J. B. Nowak; L. G. Huey; A. G. Russell; D. Tian; J. A. Neuman; D. Orsini; S. J. Sjostedt; A. P. Sullivan; D. J. Tanner; R. J. Weber; A. Nenes; E. Edgerton; F. C. Fehsenfeld

2006-01-01

10

Homogeneous nucleation of gas bubbles in vivo.  

PubMed

Several current theories of decompression sickness (DCS) presume the preexistence of gas bubble nuclei in tissue, because the de novo nucleation of gas bubbles in the body is thought to be theoretically impossible. Reexamination of nucleation theory reveals the overwhelming importance of two parameters: gas supersaturation and tissue surface tension (gamma). For the high gamma of pure water nucleation theoretically requires more than 1,000 ATA supersaturation. Lower values of gamma allow nucleation to occur with vastly smaller supersaturations. Application of homogeneous nucleation theory can provide reasonable fits to both rat and human pressure-reduction data with values of gamma within the range reported for biological fluids (below 5 dyn/cm). The initial bubble sizes predicted are 0.1 micron or less. The presence of heterogeneous sites, for example crevices and lipid surfaces, makes nucleation even more likely. PMID:6295990

Weathersby, P K; Homer, L D; Flynn, E T

1982-10-01

11

Seismic evidence for an earthquake nucleation phase  

USGS Publications Warehouse

Near-source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event. This phase was observed for the 30 earthquakes having moment magnitudes 2.6 to 8.1, and the size and duration of this phase scale with the eventual size of the earthquake. During the nucleation phase, moment release was irregular and appears to have been confined to a limited region of the fault. It was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone. These observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake.

Ellsworth, W. L.; Beroza, G. C.

1995-01-01

12

On martensitic phase nucleation with surface effects  

NASA Astrophysics Data System (ADS)

C ONTINUUM treatments of martensitic phase transitions are capable of accounting for a variety of surface effects caused by the interaction of coexisting phases of a material. Such phenomena are thought to play a critical role in determining the size, shape and stability of nucleated embryos as well as to affect the conditions under which nucleation occurs. These issues are examined within a purely mechanical context with the interaction modeled by traction and energy fields defined on the interface between phases. A class of isotropic, hyperelastic materials is introduced that is capable of modeling the dilatational component of martensitic phase transformations. Such materials are considered in a noninertial, axisymmetric setting that provides a means of exploring a variety of surface effects. Here nucleation events are modeled as deterministic, temporal shocks that are global in spatial extent, and a criterion for nucleation is suggested that is based on the energy available to create an embryo composed of a new phase. The model presented does more than capture the desired surface effects. It shows how they are related to specific assumptions regarding the constitution of interfaces. Three different types of interface are presented that serve to illustrate this.

Lusk, Mark

1994-02-01

13

Effect of dissolved gas on bubble nucleation  

Microsoft Academic Search

Experiments studying the extinction of a gas bubble in a liquid droplet and the possibility of bubble formation in a droplet containing dissolved gas are used to investigate the effect of dissolved gas on liquid-gas phase transitions (boiling, caviation, etc.). The superheat limit of the liquid was studied using a technique in which a droplet containing a dissolved gas was

Y. Mori; K. Hijikata; T. Nagatani

1976-01-01

14

Fission gas bubble nucleated cavitational swelling of the alpha-uranium phase of irradiated U-Pu-Zr fuel  

Microsoft Academic Search

Cavitational swelling has been identified as a potential swelling mechanism for the alpha uranium phase of irradiated U-Pu-Zr metal fuels for the Integral Fast Reactor being developed at Argonne National Laboratory. The trends of U-Pu-Zr swelling data prior to fuel cladding contact can be interpreted in terms of unrestrained cavitational driven swelling. It is theorized that the swelling mechanisms at

Rest

1992-01-01

15

Phase transformation kinetics in finite inhomogeneously nucleated systems  

NASA Technical Reports Server (NTRS)

Phase transformation kinetics that occur by a nucleation and growth process are investigated. A simple discrete space and time model is used for the dynamics and analytical results are obtained for the volume fraction of the material transformed for both finite systems and a special example of an inhomogeneously nucleated system. The theory is developed for two cases, initial nucleation, and continuous nucleation. The results are compared with simulations of the model.

Weinberg, Michael; Kapral, Raymond

1989-01-01

16

Nucleation and Growth of Gas Hydrate in Natural Seawater  

Microsoft Academic Search

Large-scale nucleation of gas hydrate takes place when hydrate-forming gas and seawater are brought together under suitable pressure-temperature conditions or where dissolved hydrate-forming gas in saturated or near-saturated seawater is chilled or brought to higher pressures. Profuse formation of hydrate shells on gas bubbles and nucleation of at least five different forms of gas hydrate have been achieved in fresh

S. A. Holman; J. P. Osegovic; J. C. Young; M. D. Max; A. L. Ames

2003-01-01

17

Pore-scale interfacial dynamics during gas-supersaturated water injection in porous media - on nucleation, growth and advection of disconnected fluid phases (Invited)  

Microsoft Academic Search

Degassing and in situ development of a mobile gas bubbles occur when injecting supersaturated aqueous phase into water-saturated porous media. Supersaturated water injection (SWI) has potentially significant applications in remediation of soils contaminated by non-aqueous phase liquids and in enhanced oil recovery. Pore network simulations indicate the formation of a region near the injection boundary where gas phase nuclei are

D. Or; M. Ioannidis

2010-01-01

18

Phase transition kinetics in the case of nonrandom nucleation  

Microsoft Academic Search

A theoretical model is developed for describing phase transition kinetics occurring by nucleation and growth processes. The model treats the case of spatially correlated nuclei and applies to any kind of nucleation function. A stochastic approach is employed that gives the fraction of transformed phase as a function of a series in terms of the m-dots correlation functions. Truncation of

M. Tomellini; M. Fanfoni; M. Volpe

2002-01-01

19

Nucleation of gas hydrates within constant energy systems.  

PubMed

The early stage of formation of gas hydrates has recently attracted attention as amorphous intermediate gas hydrate structures have been observed, apparently contrary to a classical model of nucleation and some experimental observations. To date, essentially all reported molecular simulations of the nucleation of gas hydrates have been under constant temperature conditions, which does not consider the possible impacts of heat transfer on the nucleation processes. Here we show, using constant energy molecular simulations, that the nuclei at an early stage of the hydrate formation have relatively more crystalline order in comparison with those observed in previous isothermal (NPT or NVT) work. The current work suggests a more transient role for intermediate amorphous structures during hydrate nucleation, thereby providing a stronger link between molecular simulation and experimental observations. Our NVE results nevertheless support the two-step nucleation mechanism proposed in previous simulation studies under constant temperature conditions which features the initial formation of amorphous hydrate-like structures. PMID:23330680

Liang, Shuai; Kusalik, Peter G

2013-02-01

20

Gas hydrate nucleation and cage formation at a water/methane interface.  

PubMed

Nucleation of gas hydrates remains a poorly understood phenomenon, despite its importance as a critical step in understanding the performance and mode of action of low dosage hydrate inhibitors. We present here a detailed analysis of the structural and mechanistic processes by which gas hydrates nucleate in a molecular dynamics simulation of dissolved methane at a methane/water interface. It was found that hydrate initially nucleates into a phase consistent with none of the common bulk crystal structures, but containing structural units of all of them. The process of water cage formation has been found to correlate strongly with the collective arrangement of methane molecules. PMID:18688529

Hawtin, Robert W; Quigley, David; Rodger, P Mark

2008-08-28

21

Determination of Gas and Vapor Nuclei for Bubble Nucleation.  

National Technical Information Service (NTIS)

Nucleation in a given liquid depends on many variables, one of the most important of which is the size distribution and concentration of gas vapor nuclei. The present work applies a new technique to the investigation of bubble nucleation and the required ...

O. Ahmed F. G. Hammitt

1968-01-01

22

Supercooling and Nucleation in Phase Transitions of the Early Universe  

NASA Astrophysics Data System (ADS)

The three phase transitions (the GUT, the electroweak and the quark-hadron), which the universe is assumed to have undergone, produce very important physical effects if they are assumed to be of first-order. It is also important that enough supercooling is produced at these transitions so that the rate of nucleation of the lower temperature phase out of the higher temperature phase is large. We argue on the basis of finitesize scaling theory that for the quark-hadron and the electroweak phase transitions the universe does not supercool enough to give sizeable nucleation rates. The nucleation probability seems to be significant only for the GUT transition.

Banerjee, B.; Gavai, R. V.

23

Void nucleation and phase stability in heavy ion irradiated materials  

Microsoft Academic Search

The response of a material to a fusion environment is one of the most important questions in fusion technology. Heavy ion irradiation can be used to further understanding of the microstructural evolution of an irradiated metal. Two aspects of heavy ion irradiation damage will be addressed: void nucleation and phase stability. A steady state void nucleation model was developed for

Plumton

1985-01-01

24

Multiscale approach to CO2 hydrate formation in aqueous solution: Phase field theory and molecular dynamics. Nucleation and growth  

Microsoft Academic Search

A phase field theory with model parameters evaluated from atomistic simulations\\/experiments is applied to predict the nucleation and growth rates of solid CO2 hydrate in aqueous solutions under conditions typical to underwater natural gas hydrate reservoirs. It is shown that under practical conditions a homogeneous nucleation of the hydrate phase can be ruled out. The growth rate of CO2 hydrate

György Tegze; Tamás Pusztai; Gyula Tóth; László Gránásy; Atle Svandal; Trygve Buanes; Tatyana Kuznetsova

2006-01-01

25

Nucleation and growth of Nb nanoclusters during plasma gas condensation  

SciTech Connect

Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

Bray, K. R.; Jiao, C. Q. [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States)] [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States); DeCerbo, J. N. [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)] [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)

2013-06-21

26

Modeling of nucleation kinetics of ternary nitrides from vapour phase  

NASA Astrophysics Data System (ADS)

Nucleation kinetics of ternary nitride layers on GaN substrate has been analysed using classical heterogeneous nucleation theory, incorporating the stress induced supercooling due to lattice mismatch between the substrate and grown layers. Using regular solution model the interfacial tension between the nucleus and substrate and hence interfacial tension between the substrate and mother phase of the compounds have been calculated. The amount of driving force available for the nucleation has been determined for different composition and the degree of supercooling. These values have been used to evaluate the nucleation parameters. It is shown that the nucleation barrier for the formation of ternary nucleus (AlGaN, InGaN and AlInN) on GaN substrate depends strongly on the composition of the alloy.

Varadarajan, E.; Dhanasekaran, R.; Ramasamy, P.

2001-08-01

27

Nucleation  

PubMed Central

Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of crystalline materials. This is particularly true for crystallization in solution, which is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. There have been significant recent advances in the understanding of the mechanism of nucleation of crystals in solution. The foremost of these are the two-step mechanism of nucleation and the notion of the solution–crystal spinodal. According to the two-step mechanism, the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, polymers, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, the significance of the dense protein liquid, and others. At high supersaturations typical of most crystallizing systems, the generation of crystal embryos occurs in the spinodal regime, where the nucleation barrier is negligible. The solution-crystal spinodal helps to understand the role of heterogeneous substrates in nucleation and the selection of crystalline polymorphs. Importantly, these ideas provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters.

Vekilov, Peter G.

2010-01-01

28

Surface tension and nucleation rate of phases of a charged colloidal suspension.  

PubMed

The square gradient approximation is used to calculate the surface tension between two phases of differing density in a charged colloidal suspension, and the results are compared with experimental and theoretical evidence from various colloidal systems. The nucleation rate of a colloidal liquid cluster from a metastable colloidal gas is estimated using a version of classical nucleation theory. We explain in terms of nucleation phenomena the recently described "Swiss cheese effect," which involves the formation of crystals from an initial disordered state, followed by the formation of disordered regions within the crystals and at the interfaces between them. We argue that this sequence of events shows evidence both of homogeneous and of heterogeneous nucleation. The experimental prominence of homogeneous nucleation suggests that metastability is very important in colloidal systems, and therefore that the consideration of nucleation rates is essential to the study of phase behavior in such systems. We also predict that the occurrence or nonoccurrence of phase separation into a dense and a rarefied phase is governed by the ratio of the macroion charge to the macroion radius. PMID:12188716

Knott, Michael; Ford, Ian J

2002-06-01

29

Adiabatic nucleation in the liquid-vapor phase transition  

NASA Astrophysics Data System (ADS)

The fundamental difference between classical (isothermal) nucleation theory (CNT) and adiabatic nucleation theory (ANT) is discussed. CNT uses the concept of isothermal heterophase fluctuations, while ANT depends on common fluctuations of the thermodynamic variables. Applications to the nonequilibrium liquid to vapor transition are shown. However, we cannot yet calculate nucleation frequencies. At present, we can only indicate at what temperatures and pressures copious homogeneous nucleation is expected in the liquid to vapor phase transition. It is also explained why a similar general indication cannot be made for the inverse vapor to liquid transition. Simultaneously, the validity of Peng-Robinson's equation of state [D.-Y. Peng and D. B. Robinson, Ind. Eng. Chem. Fundam. 15, 59 (1976)] is confirmed for highly supersaturated liquids.

de Sá, Elon M.; Meyer, Erich; Soares, Vitorvani

2001-05-01

30

Influence of thermostats and carrier gas on simulations of nucleation.  

PubMed

We investigate the influence of carrier gas and thermostat on molecular dynamics (MD) simulations of nucleation. The task of keeping the temperature constant in MD simulations is not trivial and an inefficient thermalization may have a strong influence on the results. Different thermostating mechanisms have been proposed and used in the past. In particular, we analyze the efficiency of velocity rescaling, Nose-Hoover, and a carrier gas (mimicking the experimental situation) by extensive MD simulations. Since nucleation is highly sensitive to temperature, one would expect that small variations in temperature might lead to differences in nucleation rates of up to several orders of magnitude. Surprisingly, the results indicate that the choice of the thermostating method in a simulation does not have--at least in the case of Lennard-Jones argon--a very significant influence on the nucleation rate. These findings are interpreted in the context of the classical theory of Feder et al. [Adv. Phys. 15, 111 (1966)] by analyzing the temperature distribution of the nucleating clusters. We find that the distribution of cluster temperatures is non-Gaussian and that subcritically sized clusters are colder while postcritically sized clusters are warmer than the bath temperature. However, the average temperature of all clusters is found to be always higher than the bath temperature. PMID:17705606

Wedekind, Jan; Reguera, David; Strey, Reinhard

2007-08-14

31

Gas bubble nucleation and growth in cohesive sediments  

Microsoft Academic Search

Sediment often contains a significant amount of organic material, which can be decomposed by bacterial activity. During this process and under anaerobic conditions that prevail in sediments, mainly methane and carbon dioxide are formed. These compounds will dissolve in the pore water, until the level of saturation is attained.Experiments show that gas bubble nucleation occurs already at a small oversaturation

Walther van Kesteren; Thijs van Kessel

2002-01-01

32

NUCLEATION AND GROWTH OF GAS BUBBLES IN IRRADIATED METALS  

Microsoft Academic Search

Several metals undergo nuclear reactions when subjected to neutron ; irradiation which result in the formation of gases in the metal. At elevated ; temperatures these gases tend to nucleate and form gas bubbles which result in ; over-all inportant technological implications. The available experi mental data ; on this phenomenon are rummarized, attention being concentrated on the cases of

Hickman

1960-01-01

33

Gas bubble nucleation kinetics in a live heavy oil  

Microsoft Academic Search

The current primary production of heavy oil and bitumen is highly dependent on the development of ‘foamy oil’, heavy oils containing dispersions of long-lived bubbles of gas. The nucleation and initial growth of these bubbles are key elements of the behavior of foamy oils. The tremendous levels of supersaturation associated with the expansion of live heavy oils within a porous

D. A. Lillico; A. J. Babchin; W. E. Jossy; R. P. Sawatzky; J.-Y. Yuan

2001-01-01

34

An analytical study of gas-bubble nucleation mechanisms in uranium-alloy nuclear fuel at high temperature  

Microsoft Academic Search

A multi-atom gas-bubble nucleation mechanism in uranium-alloy nuclear fuel operating in the high-temperature equilibrium gamma phase is proposed based on interpretation of measured intragranular bubble-size distribution data. This model is contrasted with the conventional two-atom nucleation mechanism within the context of a mechanistic calculation of the fission-gas bubble-size distribution. The results of the analysis enable the calculation of safety margins

J. Rest

2010-01-01

35

Gas-vapor bubble nucleation--a unified approach.  

PubMed

In a solution which is saturated with gas near the superheat limit, one might expect a bubble formed from both dissolved gas and vapor molecules to appear. The integration of the surface-energy concepts, that are postulated on completely different physical bases for gas and vapor bubble formation is a major issue. In this paper, we reformulate gas and vapor bubble nucleation by a scaling transformation, which turns the surface energy for the bubble formation from both dissolved gases and vapor molecules to the translational energy of a molecule, (3/2)kBT. With this unified approach, one could estimate the dissolved gas effect on the superheat limit of the liquid. The driving force and the molecular volume are important quantities for determining the number of gas and vapor molecules composed of a critical cluster. This approach, of course, can predict pure gas bubble formation, as well as pure vapor bubble formation, as limiting cases. Also, this approach makes it possible to find that the possible occurrence of gas bubble nucleation by dissolved gases prevents measuring the theoretical superheat limit of water at atmospheric pressure, 300 degrees C. PMID:15450464

Kwak, Ho-Young; Oh, Si-Doek

2004-10-15

36

Investigations on two-dimensional nucleation and growth kinetics of InP vapour phase epitaxy  

NASA Astrophysics Data System (ADS)

In this paper the initial stage and growth kinetics of InP vapour phase epitaxy in the In-PH 3-HCl-H 2 system have been analysed. To evaluate the two-dimensional nucleation parameters, correction due to the dependence of interfacial tension on the cluster size is included in the classical heterogeneous nucleation theory. An expression for the growth rate has been developed by following a reaction scheme in terms of deposition temperature and partial pressure of constituent gas species and so on. A numerical analysis of our theoretical results has been made.

Gopalakrishnan, N.; Dhanasekaran, R.; Ramasamy, P.

1994-03-01

37

Bubble nucleation in liquids  

Microsoft Academic Search

A review of theoretical and experimental aspects of homogeneous and heterogeneous bubble nucleation (valuable in LNG studies) covers recent developments in nucleation theory, which include hydrodynamic and diffusion constraints, gas-phase nonidealities, and heterogeneous nucleation. Large superheating may be involved in the dangerous and destructive contact vapor explosions observed in metallurgical and paper smelt processing and pose a potential hazard in

Milton Blander; Joseph L. Katz

1975-01-01

38

Nucleation and Growth of Gas Hydrate in Natural Seawater  

NASA Astrophysics Data System (ADS)

Large-scale nucleation of gas hydrate takes place when hydrate-forming gas and seawater are brought together under suitable pressure-temperature conditions or where dissolved hydrate-forming gas in saturated or near-saturated seawater is chilled or brought to higher pressures. Profuse formation of hydrate shells on gas bubbles and nucleation of at least five different forms of gas hydrate have been achieved in fresh natural seawater. Growth of masses of solid gas hydrate takes place when hydrate-forming gas reactant dissolved in seawater is brought into the vicinity of the hydrate. The gas concentration of the enriched water in the vicinity of hydrate is higher than the hydrate equilibrium gas concentration. Hydrate growth under these conditions is accelerated due to the chemical potential difference between the enriched water and the hydrate crystals, which induces mass flux of dissolved hydrate forming gas into new hydrate crystals. As long as water enriched in the hydrate-forming gas is circulated into the vicinity of the hydrate, growth proceeds into the water space. Experimental approaches for growth of examples of solid masses of hydrate are presented. Results of these experiments provide an insight into the growth of gas hydrate under natural conditions where interstitial water in marine sediments is captured by burial from open seawater, and where solid gas hydrate forms on the seafloor. By using fresh natural seawater, which is a chemically and materially complex fluid, our experiments in pressurized, refrigerated reactors should closely track the growth history of solid hydrate in the natural environment. In our model for hydrate growth in sediments, nearly complete pore fill by diagenetic hydrate can best be accomplished by nucleation of hydrate at a point source within the pore water or at a particular point on sediment particulate, with growth outward into the water space that is refreshed with ground water having high concentrations of hydrate-forming gas. Best growth can be achieved by circulation of water through constricting pore space although dissolved gas will also migrate along diffusion gradients.

Holman, S. A.; Osegovic, J. P.; Young, J. C.; Max, M. D.; Ames, A. L.

2003-12-01

39

Nucleation and growth studies of crystalline carbon phases at nanoscale  

NASA Astrophysics Data System (ADS)

Understanding the nucleation and early stage growth of crystals from the vapor phase is important for realizing large-area single-crystal quality films, controlled synthesis of nanocrystals, and the possible discovery of new phases of materials. Carbon provides the most interesting system because all its known crystalline phases (diamond, graphite and carbon nanotubes) are technologically important materials. Hence, this dissertation is focused on studying the nucleation and growth of carbon phases synthesized from the vapor phase. Nucleation experiments were performed in a microwave plasma chemical vapor deposition (CVD) reactor, and the resulting carbon nanocrystals were analyzed primarily using electron nanodiffraction and Raman spectroscopy. These studies led to the discovery of two new crystalline phases of sp 3 carbon other than diamond: face-centered and body-centered cubic carbon. Nanodiffraction results revealed possible hydrogen substitution into diamond-cubic lattices, indicating that these new phases probably act as intermediates in diamond nucleation. Nucleation experiments also led to the discovery of two new morphologies for sp2 carbon: nanocrystals of graphite and tapered, hollow 1-D structures termed here as "carbon nanopipettes". A Kinetic Monte Carlo (KMC) algorithm was developed to simulate the growth of individual diamond crystals from the vapor phase, starting with small clusters of carbon atoms (or seeds). Specifically, KMC simulations were used to distinguish the kinetic rules that give rise to a star-shaped decahedral morphology compared to decahedral crystals. KMC simulations revealed that slow adsorption on the {111} step-propagation sites compared to kink sites leads to star-decahedral crystals, and higher adsorption leads to decahedral crystals. Since the surfaces of the nanocrystals of graphite and nanopipettes were expected to be composed primarily of edge-plane sites, the electrochemical behavior of both these materials were investigated with compounds requiring chemisorption, specifically biologically important species. Both these materials exhibited a stable and reversible voltammetric behavior for dopamine (a neurotransmitter) similar to that of graphite edge planes. Furthermore, a simple bottom-up concept utilizing the tapered morphology of the nanopipettes was developed to assemble a nanoarray sensor for fast cyclic voltammetry. In summary, the main outcomes of this dissertation include: the discovery of new crystalline carbon phases, understanding kinetic faceting of multiply twinned diamond crystals and tapered morphologies of carbon nanotubes, and development of new electrode materials based on sp2 carbon nanocrystals for sensing biologically important analytes.

Mani, Radhika C.

40

Nucleation and growth of a gas bubble in magma  

NASA Astrophysics Data System (ADS)

The dynamics of a "collective" gas bubble in the magma melt during its decompression was numerically studied on the basis of a complete mathematical models of an explosive volcanic eruption. It is shown that the bubble size distribution obtained for the nucleation process has one peak, which allows considering a "collective" bubble. The main stages of bubble growth due to gas diffusion and changes in the viscosity of the medium are determined. It is shown that the high viscosity of the melt makes possible the transition from the Rayleigh equation to a simpler relation for the radial velocity of the bubble.

Davydov, M. N.

2012-05-01

41

Two lectures on phase mixing: Nucleation and symmetry restoration  

NASA Astrophysics Data System (ADS)

The dynamics of phase transitions plays a crucial rôle in the so-called interface between high energy particle physics and cosmology. Many of the interesting results generated during the last fifteen years or so rely on simplified assumptions concerning the complex mechanisms typical of nonequilibrium field theories. After reviewing well-known results concerning the dynamics of first and second order phase transitions, I argue that much is yet to be understood, in particular in situations where homogeneous nucleation theory does not apply. I present a method to deal with departures from homogeneous nucleation, and compare its efficacy with numerical simulations. Finally, I discuss the interesting problem of matching numerical simulations of stochastic field theories with continuum models.

Gleiser, Marcelo

42

Nucleation of the diamond phase in aluminium-solid solutions  

NASA Technical Reports Server (NTRS)

Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

1993-01-01

43

Theory of gas bubble nucleation in supersaturated solution of vacancies, interstitials and gas atoms  

Microsoft Academic Search

A general form of the kinetic coefficients of the Fokker–Planck equation describing gas bubble nucleation in supersaturated solution of vacancies, interstitials and gas atoms is obtained. No assumptions concerning the detailed balance are used to describe the absorption and desorption of point defects and gas atoms at the bubble surface. This allows us to investigate limits of the usual formalisms

A. E. Volkov; A. I. Ryazanov

1999-01-01

44

Electromagnetic emissions during seismic nucleation phase of stick-slips  

NASA Astrophysics Data System (ADS)

I. Introduction The size of seismic nucleation is determined by the characteristic wavelength of slip surface topography, and some scaling laws are derived from it (Ohnaka and Shen, 1999). Alternative characteristic wavelength should be introduced for natural faults because they are associated with layers of fault gouge. Riedel shear will be an equivalent since it is a characteristic structure inside fault zones. II. Method of stick- slip experiments Experimental apparatus: tri-axial apparatus. Samples: granite and gabbro cylinders of 20mmx40mm. Precut surface: 50 degree against sample axis and mirror-finished. Simulated fault gouge: quartz and gabbro powder of 0.25g. Sensors: strain gauges for measurements of axial stress and slip distance as well as three shear strain gauges pasted along a slip surface, three pairs of electrodes for measurement of triboelectric potentials. Data acquisition: continuously and synchronously at 2MHz. Experimental procedure: loading of axial stress after holding at confining pressure of 80-180 MPa and shear stress at 250 MPa during 0.1-1 hour for compaction of gouge. III. Experimental results 1) Stick-slips on bare surfaces Fluctuations of the electrode potentials during main stick-slip events are 55-180mV. Gabbro and granite samples do not show significant differences in magnitude of electrode potential. Any experimental runs were not associated with nucleation phases. Prior to main stick-slip events spike-like signals of electrode potentials were sometimes found synchronously with very small stress drops less than 1MPa. The amplitudes are less than 30mV, and they decayed exponentially. 2) Stick-slips with fault gouge Stress drops and fluctuations of electrode potentials at main stick-slip events are 7-400 MPa, 17-200mV+. Significant differences in fluctuations of electrode potentials were not found between granite and gabbro samples. About 30% of all experimental runs were associated with a nucleation phase. Slip distance, stress drop, duration and the maximum fluctuation of electrode potentials were 0.02mm, 14MPa, 0.3sec and 20mV in an experimental run, and the latter three were 3.5MPa, 0.35sec and 4mV in another run. Three pairs of strain gauges recorded the initial site and its propagation of a seismic nucleation. The potentials of three pairs of electrodes also fluctuated synchronously. The pulse-like electrode signals were sometimes found also for these experiments. IV. Discussions and conclusions 1) The reason why the stick-slips on bare surfaces were not associated with a nucleation phase is attributed to mirror-finished smooth and flat precut surfaces. 2) Irrespective of granite or gabbro powders of fault gouge, there were not significant differences in magnitude of pulse-like fluctuations of electrode potentials. This is the case for main stick-slip events. These indicate that the causes of the electric signals are not piezoelectric effect but triboelectricity and/or fracto-emission. 3) Since the fluctuations of electrode potentials are synchronous with the initiation and propagation of a nucleation, the former is attributed to the latter. 4) It is very likely that nucleation is quasi-static slip on a Riedel shear because the length of a nuclei estimated from slip during nucleation phases is the same order as the length of Riedel shears.

Onuma, K.; Otsuki, K.

2008-12-01

45

Multifold nucleation rate surfaces over phase diagrams with monotropic phase transitions  

NASA Astrophysics Data System (ADS)

The theory of supersaturated vapor nucleation for systems with monotropic polymorphic phase transitions does not entirely correspond to the modern requirements for scientific and practical applications. Semiempirical design of the nucleation rate surfaces looks like a promising way to get more reliable data for that case. Examples of the topology of nucleation rate surfaces for systems with monotropic polymorphic transitions constructed using a new concept for the semiempirical design of such surfaces over p-T phase equilibrium diagrams, where p is pressure and T is temperature, are presented.

Anisimov, M. P.; Petrova-Bogdanova, O. O.

2013-05-01

46

A Model for the Simultaneous Heterogeneous and Homogeneous Nucleation of Gas Bubbles  

Microsoft Academic Search

Electron microscope observations of cavities in steels have shown that they are often associated with microstructural features as well as occurring randomly in the matrix. Previous theoretical studies of gas bubble nucleation have concentrated on either homogeneous or heterogeneous nucleation. In the present work we extend the homogeneous nucleation rate theory for rare gases in solids to include, for the

M. R. Hayns; M. H. Wood

1979-01-01

47

Heterogeneous nucleation of fission gas bubbles and gas migration in uranium dioxide  

Microsoft Academic Search

The number and size of fission gas bubbles precipitated in irradiated uranium dioxide are calculated from a theory based on a balance between nucleation of bubbles at vacancy clusters produced by fission fragments and the agglomeration of bubbles by random motion. The distribution of bubble sizes is determined by gas atom capture, bubble agglomeration and irradiation re-solution. Irradiation re-solution exceeds

A. D. Whapham

1972-01-01

48

Can we estimate fault instability from prior phase of nucleation?  

NASA Astrophysics Data System (ADS)

We investigate the relation between interseismic stress accumulation and fault instability by numerically modeling of nucleation processes on a two-dimensional finite fault in a three-dimensional body. We assume an isolated circular homogeneous fault and the rate and state dependent friction law with both the aging and the slip types of the state evolution law. The parameter range in which we tried setting is a-b ? 0.5. To focus on the 'prior' phase of nucleation, we define Sc as a relative size of the locking center area to the whole fault, when the slip velocity on the inward creeping front reaches ten times as large as the loading rate. For the ordinary slip events, Sc can be expressed as a function of non-dimensional stability parameters, lb and lb-a. Both parameters are proportional to the product of rigidity and L, and inversely to the product of effective normal stress and fault radius. The former lb is inversely proportional to b, and the latter lb-a is to b - a. Sc is approximately given by 0.35(lb)-1 and 0.35(lb-a)-2 in case of the aging law and 0.003(lb)-3 in case of the slip law. It implies that we can certainly estimate the fault instability (particularly lb) from the area of the prior phase of nucleation. However, considering the results of the slow events in case of the aging law with 1.8 < lb-a[b-(b - a)], the relation may not be rather simple, to our regret. For the same size of Sc, there always appear two possibilities of the ordinary event and the slow event.

Mitsui, Yuta; Hirahara, Kazuro

2010-05-01

49

Bubble nucleation algorithm for the simulation of gas evolving electrodes  

Microsoft Academic Search

We propose a bubble nucleation algorithm to link a Lagrangian bubble tracker to the multi-ion transport and reaction model. This algorithm computes the bubble growth rate and the surface blocking effect at nucleation sites.

Steven Van Damme; Pedro Maciel; Heidi Van Parys; Johan Deconinck; Annick Hubin; Herman Deconinck

2010-01-01

50

Nucleation and growth in shock-induced phase transitions and how they determine wave profile features.  

PubMed

Wave profile measurement and interpretation play a central role in shock physics research. We propose an approach to revealing the direct link between the wave profile and nucleation and growth process in shock-induced phase transition. Through phase field simulations, we show for the first time that it is possible to explain experimentally measured wave profiles directly from the viewpoint of nucleation and growth, and constrain from such profiles real nucleation and growth scenarios that are otherwise impossible to study. PMID:23005645

Yu, Jidong; Wang, Wenqiang; Wu, Qiang

2012-09-14

51

Nucleation, kinetics and morphology of displacive phase transformations in iron  

NASA Astrophysics Data System (ADS)

An extensive, systematic molecular dynamics (MD) study is performed for analysing the nucleation, kinetics and morphology characteristics of thermally-induced, displacive phase transformations from face-centred cubic (fcc) to body-centred cubic (bcc) iron. At the atomic level these transformation characteristics are influenced by a number of factors, including (i) the appearance of free surfaces, (ii) the initial presence of fcc-bcc grain boundaries, (iii) the existence of point defects (i.e., atomic vacancies) near a grain boundary, (iv) the initial thermal velocities of the atoms, and (v) the specific interatomic potential used. Other MD studies that capture the overall transformation behaviour of iron well have often underestimated or ignored the influence by these factors on the transformation response, with the risk of putting the accuracy, generality and physical explanation of the MD results on loose grounds. The present research illustrates the relative contribution of each of the above factors by means of a detailed comparison study for three different interatomic potentials. The accuracy of the interatomic potentials is established by validating for the fcc and bcc phases the calculated elastic moduli, cohesive energy, vacancy formation energy and interfacial energy against experimental and ab initio data reported in the literature. The importance of calibrating material data of both the stable bcc phase and the metastable fcc phase - instead of the stable bcc phase only - is demonstrated. The numerical results call for general caution when interpreting phenomena that start close to instability points and therefore are sensitive to small disturbances; a large spread in the overall transformation time is found under different initial thermal velocities, interfacial lattice incoherence, boundary conditions (free vs. periodic), and interatomic potentials, where for completely transformed atomic systems the discrepancy between the maximum and minimum transformation time appears to be more than a factor of 150. The transformation time is phenomenologically related to the overall activation energy and the cohesive energy difference of the fcc and bcc phases, which, beyond a certain combination of values, may even prevent the transformation process from occurring. Also, the morphology of the bcc product phase is remarkably sensitive to the type of boundary conditions and the choice of interatomic potential, while the influence by both the set of initial thermal velocities and the interfacial lattice incoherence only becomes apparent for specific atomic samples that transform relatively slowly. The presence of fcc-bcc grain boundaries increases the spatial heterogeneity of transformation events, with the appearance of an increasing number of vacancies at the grain boundary giving rise to a larger overall transformation time. The 10 main results following from the present MD study are conveniently summarised at the end of this communication.

Suiker, A. S. J.; Thijsse, B. J.

2013-11-01

52

Homogeneous nucleation and macroscopic growth of gas bubble in organic solutions  

Microsoft Academic Search

This work concerns the spontaneous gas bubble nucleation after rapid decompression in organic solution initially saturated with dissolved gas and the subsequent bubble growth to macroscopic size. The decompression limit for gas bubble formation was obtained from the stability condition of the critical cluster of dissolved gas molecules. This work also clarifies how the critical cluster grows to the critical

Yong W. Kim

1998-01-01

53

Length-scale dependent variation of the first nucleated phase in nickel-silicon multilayers  

NASA Astrophysics Data System (ADS)

We have studied the first phase nucleation behavior of a series of equiatomic Ni-Si multilayers with ultrathin repeating subunits (?=1.7-5.8 nm) using x-ray reflectivity and x-ray diffraction. The variation in first nucleated phase is understood in terms of the model of Gösele and Tu, who predicted three length-scale dependent reaction routes in thin film diffusion couples: (i) For multilayers with ?>5.0 nm, interfacial nucleation of Ni2Si is observed, consistent with studies of bulk diffusion couples. (ii) For multilayers with 3.8nucleation tends towards phases richer in Si due to a waning supply of Ni within the multilayer. (iii) For multilayers with ?<2.0 nm complete mixing of the Ni-Si multilayers prefigures first phase nucleation of NiSi. In this regime the composition of the first nucleation phase is determined by the amorphous precursor, which in turn is dictated by the relative ratios of Ni and Si in the initial multilayer. A fourth scenario, between (ii) and (iii), in which Ni2Si is the first nucleated phase is also observed. A possible mechanism for this unexpected result is discussed.

Jensen, Jacob M.; Kyablue, Xavier J.; Ly, Sochetra; Johnson, David C.

2003-07-01

54

Nucleation of Gas Bubbles in Extrusion Foaming of High-Pressure Polyethylene  

Microsoft Academic Search

The nucleation of gas bubbles in extrusion foaming of high-pressure polyethylene is considered. Experiments show that undissolved gas microbubbles in the solution being foamed can have a significant effect on the number density of pores in the foam. A simple model for estimating the number density of supercritical nuclei is proposed. The effect of the time of mixing of gas

B. V. Kichatov; A. M. Korshunov

2005-01-01

55

Multiscale approach to CO2 hydrate formation in aqueous solution: phase field theory and molecular dynamics. Nucleation and growth.  

PubMed

A phase field theory with model parameters evaluated from atomistic simulations/experiments is applied to predict the nucleation and growth rates of solid CO(2) hydrate in aqueous solutions under conditions typical to underwater natural gas hydrate reservoirs. It is shown that under practical conditions a homogeneous nucleation of the hydrate phase can be ruled out. The growth rate of CO(2) hydrate dendrites has been determined from phase field simulations as a function of composition while using a physical interface thickness (0.85+/-0.07 nm) evaluated from molecular dynamics simulations. The growth rate extrapolated to realistic supersaturations is about three orders of magnitude larger than the respective experimental observation. A possible origin of the discrepancy is discussed. It is suggested that a kinetic barrier reflecting the difficulties in building the complex crystal structure is the most probable source of the deviations. PMID:16821944

Tegze, György; Pusztai, Tamás; Tóth, Gyula; Gránásy, László; Svandal, Atle; Buanes, Trygve; Kuznetsova, Tatyana; Kvamme, Bjorn

2006-06-21

56

Heterogeneous bubble nucleation and conditions for growth in a liquid–gas system of constant mass and volume  

Microsoft Academic Search

The conditions are considered under which heterogeneous bubble nucleation takes place in a conical pit in the boundary of a constant size volume containing a liquid–gas solution, and the size to which the nucleate bubble grows is predicted. Four possible equilibrium states are found for the nucleate bubble: two unstable, one metastable, and one stable. The unstable state corresponding to

C. A. Ward; W. R. Johnson; R. D. Venter; S. Ho; T. W. Forest; W. D. Fraser

1983-01-01

57

Gas-liquid nucleation at large metastability: unusual features and a new formalism  

NASA Astrophysics Data System (ADS)

Nucleation at large metastability is still largely an unsolved problem, even though it is a problem of tremendous current interest, with wide-ranging practical value, from atmospheric research to materials science. It is now well accepted that the classical nucleation theory (CNT) fails to provide a qualitative picture and gives incorrect quantitative values for such quantities as activation-free energy barrier and supersaturation dependence of nucleation rate, especially at large metastability. In this paper, we present an alternative formalism to treat nucleation at large supersaturation by introducing an extended set of order parameters in terms of the kth largest liquid-like clusters, where k = 1 is the largest cluster in the system, k = 2 is the second largest cluster and so on. At low supersaturation, the size of the largest liquid-like cluster acts as a suitable order parameter. At large supersaturation, the free energy barrier for the largest liquid-like cluster disappears. We identify this supersaturation as the one at the onset of kinetic spinodal. The kinetic spinodal is system-size-dependent. Beyond kinetic spinodal many clusters grow simultaneously and competitively and hence the nucleation and growth become collective. In order to describe collective growth, we need to consider the full set of order parameters. We derive an analytic expression for the free energy of formation of the kth largest cluster. The expression predicts that, at large metastability (beyond kinetic spinodal), the barrier of growth for several largest liquid-like clusters disappears, and all these clusters grow simultaneously. The approach to the critical size occurs by barrierless diffusion in the cluster size space. The expression for the rate of barrier crossing predicts weaker supersaturation dependence than what is predicted by CNT at large metastability. Such a crossover behavior has indeed been observed in recent experiments (but eluded an explanation till now). In order to understand the large numerical discrepancy between simulation predictions and experimental results, we carried out a study of the dependence on the range of intermolecular interactions of both the surface tension of an equilibrium planar gas-liquid interface and the free energy barrier of nucleation. Both are found to depend significantly on the range of interaction for the Lennard-Jones potential, both in two and three dimensions. The value of surface tension and also the free energy difference between the gas and the liquid phase increase significantly and converge only when the range of interaction is extended beyond 6-7 molecular diameters. We find, with the full range of interaction potential, that the surface tension shows only a weak dependence on supersaturation, so the reason for the breakdown of CNT (with simulated values of surface tension and free energy gap) cannot be attributed to the supersaturation dependence of surface tension. This remains an unsettled issue at present because of the use of the value of surface tension obtained at coexistence.

Santra, Mantu; Singh, Rakesh S.; Bagchi, Biman

2011-03-01

58

Nucleation of ordered solid phases of proteins via a disordered high-density state: phenomenological approach.  

PubMed

Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed. PMID:15910067

Pan, Weichun; Kolomeisky, Anatoly B; Vekilov, Peter G

2005-05-01

59

Localized Orientational Order Chaperones the Nucleation of Rotator Phases in Hard Polyhedral Particles  

NASA Astrophysics Data System (ADS)

The nucleation kinetics of the rotator phase in hard cuboctahedra, truncated octahedra, and rhombic dodecahedra is simulated via a combination of forward flux sampling and umbrella sampling. For comparable degrees of supersaturation, the polyhedra are found to have significantly lower free-energy barriers and faster nucleation rates than hard spheres. This difference primarily stems from localized orientational ordering, which steers polyhedral particles to pack more efficiently. Orientational order hence fosters here the growth of orientationally disordered nuclei.

Thapar, Vikram; Escobedo, Fernando A.

2014-01-01

60

Gas–vapor bubble nucleation—a unified approach  

Microsoft Academic Search

In a solution which is saturated with gas near the superheat limit, one might expect a bubble formed from both dissolved gas and vapor molecules to appear. The integration of the surface-energy concepts, that are postulated on completely different physical bases for gas and vapor bubble formation is a major issue. In this paper, we reformulate gas and vapor bubble

Ho-Young Kwak; Si-Doek Oh

2004-01-01

61

Competition of homogeneous and heterogeneous ice nucleation on secondary organic aerosol particles: The role of particle phase state  

NASA Astrophysics Data System (ADS)

Recently, secondary organic aerosol (SOA) particles have been found to exhibit a highly viscous, amorphous state under atmospherically relevant conditions (Virtanen et al., 2010). Besides retardation of chemical reactions (Shiraiwa et al., 2011) and incomplete gas-to-particle partitioning of semi-volatile constituents (Vaden et al., 2011), these particles were found to suppress homogeneous ice nucleation (Murray et al., 2008), which normally takes place when a liquid particle reaches its respective homogeneous nucleation limit (Koop et al., 2000). In turn, glassy SOA particles may act themselves as heterogeneous ice nuclei as recent studies suggest (e.g. Murray et al., 2010, Wang et al., 2012). The predominant nucleation pathway for SOA particles is thus controlled by particle phase state. The phase state of SOA particles depends on several factors such as composition, temperature and relative humidity. In atmospheric updrafts, inducing a change in temperature and relative humidity, moisture- and temperature-induced phase transitions can occur (e.g. Shiraiwa et al., 2011). In fast updrafts, these particles may also deviate from humidification equilibrium, i.e. the agreement between ambient relative humidity and water activity inside the particle may not be established at any point in time. The extent of this temporal delay is governed by the updraft velocity, the particle size and the diffusivity of water inside the glassy organic particle matrix. Here we show how the delayed deliquescence of SOA particles can be quantified for SOA from a variety of precursors. A kinetic flux model (Shiraiwa et al., 2012) is applied and the predominant ice nucleation pathway is inferred from particle phase state at the respective homogeneous and heterogeneous nucleation limits. To estimate diffusivities inside the organic particle matrix for the relevant range of temperature and humidity, we developed a novel method that relies on glass transition and hygroscopic growth data that are more easily available. The model simulations suggest upper temperature boundaries, below which heterogeneous ice nucleation of glassy aerosols may occur, depending on updraft velocities and particle size. We also show that the predominant ice nucleation pathway depends on precursor material and oxidation state. References Koop, T. et al. (2000) Nature 406, 611. Murray, B. J. (2008) Atmos. Chem. Phys. 8, 5423. Murray, B. J. et al. (2010) Nature Geosci. 3, 233. Shiraiwa, M. et al. (2011) Proc. Natl. Acad. Sci. 108, 11003. Shiraiwa, M. et al. (2012) Atmos. Chem. Phys. 12, 2777. Virtanen, A. et al. (2010) Nature 467, 824. Vaden, T. D. et al. (2011) Proc. Natl. Acad. Sci., 108, 2190. Wang, B. et al. (2012) J. Geophys. Res., 117, D16209.

Berkemeier, Thomas; Shiraiwa, Manabu; Pöschl, Ulrich; Koop, Thomas

2014-05-01

62

Role of nucleation and growth in two-phase microstructure formation  

NASA Astrophysics Data System (ADS)

During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different oscillatory microstructures that depend on the imposed velocity and the size of the sample. At low thermal gradient to velocity ratio, a steady-state composite microstructure is observed. Two mechanisms of composite microstructure formation were examined: (i) the formation of the peritectic phase in the intercellular region of the primary phase where the solute rejected by the primary phase is absorbed by the peritectic phase. The peritectic phase forms a small distance behind the growing primary phase front. (ii) The second mechanism is the coupled growth of the two phases with a macroscopically planar interface, as in the case of eutectic growth. Detailed studies showed that this composite microstructure, although it appears as a eutectic microstructure, did not grow in the coupled manner at the advancing interface in the Sn-Cd system. However, a new observation was made when experiments were carried out in thin ampoule of Ta. The peritectic phase nucleated at the wall-interface triple junction and grew along the wall, while the primary phase continued to grow at the center, giving rise to a steady-state couple growth at some specific velocity. The mechanism of coupled growth in this case was shown to be operative due to the presence of a finite contact angle at the wall, and this was demonstrated by including the contact angle effect at the wall in the rod eutectic growth model. The experimental results were summarized to map out the conditions of thermal gradient and velocity on the regimes of composite and oscillatory microstructure formation. The formation of complex time-dependent microstructures was then discussed in terms of the time-dependent dynamics of planar interface growth.

Shin, Jong Ho

63

Theoretical study of vapor-liquid homogeneous nucleation using stability analysis of a macroscopic phase.  

PubMed

Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models. PMID:23061836

Carreón-Calderón, Bernardo

2012-10-14

64

Nucleation of the CO2 hydrate from three-phase contact lines.  

PubMed

Using molecular dynamics simulations on the microsecond time scale, we investigate the nucleation and growth mechanisms of CO(2) hydrates in a water/CO(2)/silica three-phase system. Our simulation results indicate that the CO(2) hydrate nucleates near the three-phase contact line rather than at the two-phase interfaces and then grows along the contact line to form an amorphous crystal. In the nucleation stage, the hydroxylated silica surface can be understand as a stabilizer to prolong the lifetime of adsorbed hydrate cages that interact with the silica surface by hydrogen bonding, and the adsorbed cages behave as the nucleation sites for the formation of an amorphous CO(2) hydrate. After nucleation, the nucleus grows along the three-phase contact line and prefers to develop toward the CO(2) phase as a result of the hydrophilic nature of the modified solid surface and the easy availability of CO(2) molecules. During the growth process, the population of sI cages in the formed amorphous crystal is found to increase much faster than that of sII cages, being in agreement with the fact that only the sI hydrate can be formed in nature for CO(2) molecules. PMID:22551251

Bai, Dongsheng; Chen, Guangjin; Zhang, Xianren; Wang, Wenchuan

2012-05-22

65

Nucleation and Growth of Gas Bubbles in Elastomers  

Microsoft Academic Search

An experimental study is described of the formation and growth of gas bubbles in crosslinked elastomers. A critical condition for bubble formation is found to hold in most cases: The gas supersaturation pressure must exceed 5G?2, where G is the shear modulus of the elastomer. The kinetics of bubble growth are shown to be in good accord with a simple

A. N. Gent; D. A. Tompkins

1969-01-01

66

Collector phase transitions during vapor-solid-solid nucleation of GaN nanowires.  

PubMed

We investigate the nucleation of Ni-induced GaN nanowires by in situ and ex situ experiments. Three nucleation stages are evidenced. In the first two stages, different crystal structures of the Ni collectors are identified. Real-time monitoring of the Ga desorption allows the amount of Ga incorporated in the collectors to be quantified. A transition of their crystal structure prior to nanowire growth is found to be in agreement with the thermodynamically stable phase sequence of the relevant phase diagrams. PMID:20715843

Chèze, Caroline; Geelhaar, Lutz; Trampert, Achim; Brandt, Oliver; Riechert, Henning

2010-09-01

67

On the nucleation and composition analysis of InAs 1- xP x during vapour phase epitaxial growth  

NASA Astrophysics Data System (ADS)

The present investigation deals with the nucleation and growth kinetics of InAs 1- xP x vapour phase epitaxy in In?HCl?AsH 3?PH 3?H 2 systems. The expressions for the critical nucleation parameters are evaluated as a function of surface tension, supercooling and the composition of the alloy and it is found that the (100) orientation has the highest critical nucleation barriers. The expression for the layer composition has been derived in terms of growth rates of InP and InAs, which in turn derived in terms of partial pressures and deposition temperature. The influence of the input gas mole ratio ( {PH3}/{( PH3 + AsH3) }) and the deposition temperature on the layer composition has been investigated in detail. It is found that the composition is more strongly affected by the gas mole ratio than the deposition temperature, and As is more preferentially deposited than P. Our theoretical findings are compared with the experimental reports and there is a good agreement between them.

Gopalakrishnan, N.; Dhanasekaran, R.

1996-05-01

68

The influence of additives and metal rods on the nucleation and growth of gas hydrates.  

PubMed

A major technical issue in industrial applications of the gas hydrate storage process is to develop a practical means for rapid hydrate formation. In this paper, the formation processes of HCFC141b (CH(3)CCl(2)F) gas hydrate in a column of water with additives and with an iron rod that was placed in the center of the column have been studied to reveal the influence of the additives and the iron rod on the nucleation and growth of the gas hydrate. The water solution column, in a cylindrical glass container, was placed in a thermostatic bath at 274.15-280.15 K and under atmospheric pressure. The experimental results show that, compared to the pure water and the HCFC141b system, the properly placed iron rod combined with proper concentrations of lauryl sodium sulfonate, lauryl sodium sulfate, and sodium dodecylbenzenesulfonate-6 considerably reduces the hydrate nucleation time and promotes formation speed. The formation rate of HCFC141b gas hydrate increases with increasing concentration of sodium dodecylbenzenesulfonate-6 in the water solution, while the addition of potassium oxalate monohydrate in water has shown no effect on the nucleation and growth of HCFC141b gas hydrate. Under the experimental conditions, both the anion surfactants and the iron rod strongly induce the first nucleation of HCFC141b gas hydrate, while the following growth of the HCFC141b gas hydrate is primarily influenced by the anion surfactant. This experiment suggests a new way of fast formation of clathrate hydrate, which may be much easier for practical application of the gas hydrate for cold storage in air conditioning systems. PMID:15694442

Li, Jinping; Liang, Deqing; Guo, Kaihua; Wang, Ruzhu

2005-03-01

69

Experiments on fast nucleation and growth of HCFC141b gas hydrate in static water columns  

Microsoft Academic Search

A major technical issue in the realization of refrigerants gas hydrates energy storage systems is to develop a practical means for rapid hydrate formation. In this paper, the nucleation and growth processes of HCFC141b (CH3CCl2F, HCFC141b) gas hydrate in a column of water added with 0.038wt% sodium dodecylbenzenesulfonate-6 and with a metal rod which was placed in the center of

Jinping Li; Kaihua Guo; Deqing Liang; Ruzhu Wang

2004-01-01

70

Transient nucleation kinetics of crystal growth at the intermediate stage of bulk phase transitions  

NASA Astrophysics Data System (ADS)

A complete analytical solution of an integro-differential model describing the transient nucleation of solid particles and their subsequent growth at the intermediate stage of phase transitions in metastable systems is constructed. A Fokker-Plank type equation for the density distribution function is solved exactly for arbitrary nucleation kinetics. A non-linear integral equation with memory kernel connecting the density distribution function and the system supercooling/supersaturation is analytically solved on the basis of the saddle-point method for the Laplace integral. The analytical solution obtained shows that the process at the intermediate stage is divided into three phases: initially the high rate nucleation stage occurs, then this process is accompanied by the particle growth reducing the level of metastability, and finally the mechanism of particle coarsening becomes predominant.

Alexandrov, D. V.; Malygin, A. P.

2013-11-01

71

Kinetics of the initial stage of isothermal gas phase formation  

SciTech Connect

A theoretical description is proposed of the kinetics of the initial stage of gas phase formation in supersaturated liquids at constant temperature. General expressions are given for the time dependence of the number [ital N] of bubbles nucleated, of the probability [ital P] of appearance of at least one nucleus bubble and of the total volume [ital V][sub [ital g

Kashchiev, D.; Firoozabadi, A. (Reservoir Engineering Research Institute, Palo Alto, California 94304 (United States))

1993-03-15

72

Random-walk Monte Carlo simulation of intergranular gas bubble nucleation in UO2 fuel  

NASA Astrophysics Data System (ADS)

Using a random-walk particle algorithm, we investigate the clustering of fission gas atoms on grain boundaries in oxide fuels. The computational algorithm implemented in this work considers a planar surface representing a grain boundary on which particles appear at a rate dictated by the Booth flux, migrate two dimensionally according to their grain boundary diffusivity, and coalesce by random encounters. Specifically, the intergranular bubble nucleation density is the key variable we investigate using a parametric study in which the temperature, grain boundary gas diffusivity, and grain boundary segregation energy are varied. The results reveal that the grain boundary bubble nucleation density can vary widely due to these three parameters, which may be an important factor in the observed variability in intergranular bubble percolation among grain boundaries in oxide fuel during fission gas release.

Millett, Paul C.; Zhang, Yongfeng; Andersson, D. A.; Tonks, Michael R.; Biner, S. B.

2012-11-01

73

Adiabatic nucleation  

NASA Astrophysics Data System (ADS)

A simple adiabatic nucleation model, based on an extended Mollier (enthalpy-entropy) diagram, predicts a definite stability limit for the liquid-solid phase transition and is in good agreement with the lowest known experimental supercooling temperatures of low viscosity liquids. In the case of liquid gallium this model also correctly predicts that, at maximum supercooling, the metastable phase Ga ? will nucleate rather than the stable phase Ga ? or the metastable phase Ga ?.

Meyer, Erich

1986-03-01

74

Bubble nucleation in viscous material due to gas formation by a chemical reaction: application to coal pyrolysis  

Microsoft Academic Search

Most coals swell when heated, and their plastic properties change. These phenomena are explained qualitatively and semiquantitatively using a theory which combines classical nucleation theory and chemical kinetics. Classical bubble nucleation theory is modified to include cases where gases are formed in a liquid as a result of a chemical reaction. Part of the gas that is formed in the

Amir Attar

1978-01-01

75

Phase nucleation and growth mechanisms during the solidification of Fe-B hypoeutectic alloys under melt-quenching conditions  

NASA Astrophysics Data System (ADS)

The solidification laws of hypoeutectic alloys Fe-B during rapid cooling are studied. The solidification mechanisms of heterogeneous and homogeneous nucleation and the following crystal growth are considered depending on the cooling rate of a melt layer and the conditions before the solidification front. The nucleation conditions for different types of borides and ? and ?-Fe are studied. The relation between the type and morphology of the forming crystalline phases and the temperature-concentration conditions of their nucleation and growth is shown.

Volkov, V. A.; Suslov, A. A.

2008-10-01

76

Classical nucleation theory with a radius-dependent surface tension: A two-dimensional lattice-gas automata model  

NASA Astrophysics Data System (ADS)

The constant surface tension assumption of the Classical Nucleation Theory (CNT) is known to be flawed. In order to probe beyond this limitation, we consider a microscopic, two-dimensional Lattice-Gas Automata (LGA) model of nucleation in a supersaturated system, with model input parameters Ess (solid particle-to-solid particle bonding energy), Esw (solid particle-to-water bonding energy), ? (next-to-nearest-neighbor bonding coefficient in solid phase), and Cin (initial solute concentration). The LGA method has the advantages of easy implementation, low memory requirements, and fast computation speed. Analytical results for the system's concentration and the crystal radius as functions of time are derived and the former is fit to the simulation data in order to determine the equilibrium concentration. The “Mean First-Passage Time” technique is used to obtain the nucleation rate and critical nucleus size from the simulation data. The nucleation rate and supersaturation data are evaluated using a modification to the CNT that incorporates a two-dimensional radius-dependent surface tension term. The Tolman parameter, ?, which controls the radius dependence of the surface tension, decreases (increases) as a function of the magnitude of Ess (Esw), at fixed values of ? and Esw (Ess). On the other hand, ? increases as ? increases while Ess and Esw are held constant. The constant surface tension term of the CNT, ?0, increases (decreases) with increasing magnitudes of Ess (Esw) at fixed values of Esw (Ess) and increases as ? is increased. ?0 increases linearly as a function of the change in energy during an attachment or detachment reaction, |?E|, however, with a slope less than that predicted for a crystal that is uniformly packed at maximum density. These results indicate an increase in the radius-dependent surface tension, ?, with respect to increasing magnitude of the difference between Ess and Esw.

Hickey, Joseph; L'Heureux, Ivan

2013-02-01

77

Observation of the seismic nucleation phase in the Ridgecrest, California, earthquake sequence  

USGS Publications Warehouse

Near-source observations of five M 3.8-5.2 earthquakes near Ridgecrest, California are consistent with the presence of a seismic nucleation phase. These earthquakes start abruptly, but then slow or stop before rapidly growing again toward their maximum rate of moment release. Deconvolution of instrument and path effects by empirical Green's functions demonstrates that the initial complexity at the start of the earthquake is a source effect. The rapid growth of the P-wave arrival at the start of the seismic nucleation phase supports the conclusion of Mori and Kanamori [1996] that these earthquakes begin without a magnitude-scaled slow initial phase of the type observed by Iio [1992, 1995].

Ellsworth, W. L.; Beroza, G. C.

1998-01-01

78

Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses  

SciTech Connect

Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.

Pavlov, Konstantin M. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); School of Physics, Monash University, Victoria 3800 (Australia); Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Vine, David J. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, The University of Melbourne, Parkville, Victoria 3010 (Australia); Schmalz, Jelena A. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); Suzuki, Yoshio; Uesugi, Kentaro; Takeuchi, Akihisa; Yagi, Naoto [SPring-8/JASRI (Japan Synchrotron Radiation Research Institute), Hyogo 679-5198 (Japan); Kharchenko, Alexander; Blaj, Gabriel [PANalytical B.V., P.O. Box 13, 7600 AA Almelo (Netherlands); Jakubek, Jan [Institute of Experimental and Applied Physics, Czech Technical University in Prague, 166 36 Prague 6 (Czech Republic); Altissimo, Matteo [Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, Victoria 3168 (Australia); Materials Science and Engineering, Commonwealth Scientific and Industrial Research Organisation, Clayton South, Victoria 3169 (Australia); Clark, Jesse N. [London Centre for Nanotechnology, University College, Gower St, London WC1E 6BT (United Kingdom)

2011-01-15

79

Nucleation of AgInSbTe films employed in phase-change media  

SciTech Connect

In phase-change technology small volumes of a chalcogenide material are switched between amorphous and crystalline states by local heating with a short laser or current pulses. AgInSbTe is an alloy frequently used in optical data storage, which could also be applied in electronic data storage. For those applications it is crucial to understand the reliability and reproducibility of the switching process. In this work the first crystallization of an AgInSbTe alloy has been studied on a microsecond time scale using a focused laser beam. The experiments show that nucleation is a process governed by statistics. A correlation between the success of a nucleation event with the probability of nucleation is established. By measuring the nucleation probability as a function of laser pulse duration, the incubation time is determined to 11 {mu}s. The results are compared to measurements of the growth velocity of this material. The analysis of the temperature dependence of the growth velocity explains why AgInSbTe shows growth-dominated recrystallization. The implications of these findings to the application of such growth-dominated materials in electronic data storage are discussed.

Ziegler, Stefan; Wuttig, Matthias [Institute of Physics (IA), RWTH Aachen University, 52056 Aachen (Germany)

2006-03-15

80

Bubble nucleation in first-order inflation and other cosmological phase transitions  

SciTech Connect

We address in some detail the kinematics of bubble nucleation and percolation in first-order cosmological phase transitions, with the primary focus on first-order inflation. We study how a first-order phase transition completes, describe measures of its progress, and compute the distribution of bubble sizes. For example, we find that the typical bubble size in a successful transition is of order 1% to 100% of the Hubble radius, and depends very weakly on the energy scale of the transition. We derive very general conditions that must be satisfied by {Gamma}/{ital H}{sup 4} to complete the phase transition ({Gamma}=bubble nucleation rate per unit volume; {ital H}=expansion rate; physically, {Gamma}/{ital H}{sup 4} corresponds to the volume fraction of space occupied by bubbles nucleated over a Hubble time). In particular, {Gamma}/{ital H}{sup 4} must exceed 9/4{pi} to successfully end inflation. To avoid the deleterious effects of bubbles nucleated early during inflation on primordial nucleosynthesis and on the isotropy and spectrum of the cosmic microwave background radiation, during most of inflation {Gamma}/{ital H}{sup 4} must be less than order 10{sup {minus}4}--10{sup {minus}3}. Our constraints imply that in a successful model of first-order inflation the phase transition must complete over a period of at most a few Hubble times and all but preclude individual bubbles from providing an interesting source of density perturbation. We note, though, that it is just possible for Poisson fluctuations in the number of moderately large-size bubbles to lead to interesting isocurvature perturbations, whose spectrum is not scale invariant. Finally, we analyze in detail several recently proposed models of first-order inflation.

Turner, M.S. (NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States) Departments of Physics and Astronomy ( ) Astrophysics, Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637-1433 (United States)); Weinberg, E.J. (NASA/Fermilab Astrophysics Center and Theory Group, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States) Department of Physics, Columbia University, New York, New York 10027 (United States) School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States)); Widrow, L.M. (Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario, M5S1A1 (Canada))

1992-09-15

81

Phase-field simulations of gas density within bubbles in metals under irradiation  

Microsoft Academic Search

Phase-field simulations are used to study the evolution of gas density within irradiation-induced bubbles in solids. In our simulations, which use copper as a model material, the dpa rate, gas production rate, and defect diffusivities are systematically varied to understand their effect on bubble nucleation rates, bubble densities, and the distribution of gas concentration within bubbles and in the solid

Paul C. Millett; Michael Tonks

2011-01-01

82

Decay of a Metastable Cylinder Phase via Nucleation of the Stable Lamellar Phase in a Diblock Copolymer Melt  

NASA Astrophysics Data System (ADS)

We simulate the time-dependent Landau-Brazovskii equation in three dimensions and study the kinetics of a lamellar phase nucleating from a metastable cylinder phase in a diblock copolymer melt. The underlying microstructure leads to a complicated droplet interface structure, an orientation-dependent interfacial velocity, and non-spherical nuclei. In part, our motivation is to compare with an earlier nucleation theory by Wickham, Shi and Wang (2003), which uses approximations not present in our simulations. Our numerically computed droplet shape compares well with the theory, as do our critical volume and free-energy near coexistence. Farther from coexistence, the droplet shape is more spherical, and the critical volume is larger than theory predicts. We go beyond the static theory to find the orientation-dependent interface velocity and droplet growth rates, the fastest of which is in the direction normal to the lamellae.

Spencer, Russell; Wickham, Robert

2010-03-01

83

Development of a high pressure automated lag time apparatus for experimental studies and statistical analyses of nucleation and growth of gas hydrates.  

PubMed

Nucleation in a supercooled or a supersaturated medium is a stochastic event, and hence statistical analyses are required for the understanding and prediction of such events. The development of reliable statistical methods for quantifying nucleation probability is highly desirable for applications where control of nucleation is required. The nucleation of gas hydrates in supercooled conditions is one such application. We describe the design and development of a high pressure automated lag time apparatus (HP-ALTA) for the statistical study of gas hydrate nucleation and growth at elevated gas pressures. The apparatus allows a small volume (?150 ?l) of water to be cooled at a controlled rate in a pressurized gas atmosphere, and the temperature of gas hydrate nucleation, T(f), to be detected. The instrument then raises the sample temperature under controlled conditions to facilitate dissociation of the gas hydrate before repeating the cooling-nucleation cycle again. This process of forming and dissociating gas hydrates can be automatically repeated for a statistically significant (>100) number of nucleation events. The HP-ALTA can be operated in two modes, one for the detection of hydrate in the bulk of the sample, under a stirring action, and the other for the detection of the formation of hydrate films across the water-gas interface of a quiescent sample. The technique can be applied to the study of several parameters, such as gas pressure, cooling rate and gas composition, on the gas hydrate nucleation probability distribution for supercooled water samples. PMID:21721732

Maeda, Nobuo; Wells, Darrell; Becker, Norman C; Hartley, Patrick G; Wilson, Peter W; Haymet, Anthony D J; Kozielski, Karen A

2011-06-01

84

Development of a high pressure automated lag time apparatus for experimental studies and statistical analyses of nucleation and growth of gas hydrates  

NASA Astrophysics Data System (ADS)

Nucleation in a supercooled or a supersaturated medium is a stochastic event, and hence statistical analyses are required for the understanding and prediction of such events. The development of reliable statistical methods for quantifying nucleation probability is highly desirable for applications where control of nucleation is required. The nucleation of gas hydrates in supercooled conditions is one such application. We describe the design and development of a high pressure automated lag time apparatus (HP-ALTA) for the statistical study of gas hydrate nucleation and growth at elevated gas pressures. The apparatus allows a small volume (~150 ?l) of water to be cooled at a controlled rate in a pressurized gas atmosphere, and the temperature of gas hydrate nucleation, Tf, to be detected. The instrument then raises the sample temperature under controlled conditions to facilitate dissociation of the gas hydrate before repeating the cooling-nucleation cycle again. This process of forming and dissociating gas hydrates can be automatically repeated for a statistically significant (>100) number of nucleation events. The HP-ALTA can be operated in two modes, one for the detection of hydrate in the bulk of the sample, under a stirring action, and the other for the detection of the formation of hydrate films across the water-gas interface of a quiescent sample. The technique can be applied to the study of several parameters, such as gas pressure, cooling rate and gas composition, on the gas hydrate nucleation probability distribution for supercooled water samples.

Maeda, Nobuo; Wells, Darrell; Becker, Norman C.; Hartley, Patrick G.; Wilson, Peter W.; Haymet, Anthony D. J.; Kozielski, Karen A.

2011-06-01

85

Molecular Dynamics of Simulation of the Nucleation, Growth, Inhibition and Control of Gas Hydrates. Annual Report, April 1991-March 1992.  

National Technical Information Service (NTIS)

This is the first annual report for the Gas Research Institute-funded contract (number 5091-860-2125) entitled 'Molecular Dynamics of Gas Hydrate Nucleation, Growth, Inhibition and Control', covering the period 4/1/91-4/1/92. There were two main objective...

P. Clancy

1992-01-01

86

AIDA experiments on heterogeneous ice nucleation in warm mixed-phase clouds  

NASA Astrophysics Data System (ADS)

Clouds are important regulators of the Earth's temperature, because they scatter shortwave radiation from the sun back to space (cooling effect) and absorb long wave terrestrial radiation from the Earth surface (warming effect). About 60% of the Earth's surface is covered with clouds at any time. The response of cloud characteristics and precipitation processes to changing natural and anthropogenic aerosol sources is one of the largest uncertainties in the current understanding of climate change. Cloud development and precipitation are related to a complex chain of microphysical processes which in many cases starts with the formation of the ice phase. The occurrence and abundance of the ice phase in tropospheric clouds is strongly linked to the freezing properties of cloud droplets and aerosol solution particles as well as the abundance and properties of insoluble aerosol particles which selectively act as heterogeneous ice nuclei. Field and laboratory work have demonstrated that in particular mineral dust and bological particles can act as heterogeneous ice nuclei in mixed-phase clouds. Little is known however about the ice nucleation impact of organic matter, which has been found as a prominent compound of tropospheric aerosol particles and has the potential to form surface coatings to other aerosol particles during their transport through the atmosphere. The AIDA (Aerosol Interaction and Dynamics in the Atmosphere) facility at the Karlsruhe Institute of Technology has been used to investigate the heterogeneous ice nucleation efficiency of various dust and biological particles. The temperature, pressure and humidity conditions in the cloud chamber can be varied in a wide range of natural cloud systems. This is achieved by expansion cooling induced by strong pumping to the chamber volume. This talk will summarise AIDA experiments and results on the ice nucleation behaviour of bacteria, mineral dust particles, and dust particles coated with sulphuric acid and secondary organic aerosol (SOA) mass from the reaction of alpha-pinene with ozone.

Möhler, Ottmar; Benz, Stefan; Leisner, Thomas; Niemand, Monika; Oehm, Caroline; Saathoff, Harald; Schnaiter, Martin; Wagner, Robert

2010-05-01

87

On the theory of transient nucleation at the intermediate stage of phase transitions  

NASA Astrophysics Data System (ADS)

The evolution of a system of growing aggregates in a macroscopically homogeneous medium with account of both the reduction in metastability and the continuing initiation of new nuclei is studied. The corresponding integro-differential model describing the intermediate stage of phase transitions is solved analytically for arbitrary nucleation kinetics and growth rates of nuclei. An exact solution of the Fokker–Planck equation is found with allowance for the diffusivity along the axis of nucleus radii. In limiting cases of purely kinetic and mixed kinetic-diffusion rates of crystal growth for a special form of diffusivity, the obtained solutions transform to earlier known expressions.

Alexandrov, D. V.

2014-04-01

88

Classical nucleation theory with a radius-dependent surface tension: a two-dimensional lattice-gas automata model.  

PubMed

The constant surface tension assumption of the Classical Nucleation Theory (CNT) is known to be flawed. In order to probe beyond this limitation, we consider a microscopic, two-dimensional Lattice-Gas Automata (LGA) model of nucleation in a supersaturated system, with model input parameters E(ss) (solid particle-to-solid particle bonding energy), E(sw) (solid particle-to-water bonding energy), ? (next-to-nearest-neighbor bonding coefficient in solid phase), and C(in) (initial solute concentration). The LGA method has the advantages of easy implementation, low memory requirements, and fast computation speed. Analytical results for the system's concentration and the crystal radius as functions of time are derived and the former is fit to the simulation data in order to determine the equilibrium concentration. The "Mean First-Passage Time" technique is used to obtain the nucleation rate and critical nucleus size from the simulation data. The nucleation rate and supersaturation data are evaluated using a modification to the CNT that incorporates a two-dimensional radius-dependent surface tension term. The Tolman parameter, ?, which controls the radius dependence of the surface tension, decreases (increases) as a function of the magnitude of E(ss) (E(sw)), at fixed values of ? and E(sw) (E(ss)). On the other hand, ? increases as ? increases while E(ss) and E(sw) are held constant. The constant surface tension term of the CNT, ?(0), increases (decreases) with increasing magnitudes of E(ss) (E(sw)) at fixed values of E(sw) (E(ss)) and increases as ? is increased. ?(0) increases linearly as a function of the change in energy during an attachment or detachment reaction, |?E|, however, with a slope less than that predicted for a crystal that is uniformly packed at maximum density. These results indicate an increase in the radius-dependent surface tension, ?, with respect to increasing magnitude of the difference between E(ss) and E(sw). PMID:23496525

Hickey, Joseph; L'Heureux, Ivan

2013-02-01

89

The bcc-hcp Phase Transition in 4He: Comparison with the Theory of Homogeneous Nucleation  

NASA Astrophysics Data System (ADS)

Precise pressure experiments in supercooled bcc 4He are carried out under cooling along an isochore near an equilibrium line of the bcc-hcp structural phase transition. It is established that the transition from bcc to hcp occurs after significant delay which can be of a few seconds to a few hours depending on the extent of supercooling. The data obtained allow to establish of a line of maximum supercooling in the P-T phase diagram and to describe it within the framework of homogeneous nucleation theory. It is shown that the reverse hcp-bcc transition occurs without any delay, i.e., this structural phase transition is strongly asymmetric. The additional peculiarities are observed in the pressure and temperature time dependences. The possible reasons appearing of them are discussed

Grigor'ev, V. N.; Mikhin, N. P.; Rudavskii, E. Y.; Vekhov, Y. O.

2008-01-01

90

Report on the Implementation of Homogeneous Nucleation Scheme in MARMOT-based Phase Field Simulation  

SciTech Connect

In this report, we summarized our effort in developing mesoscale phase field models for predicting precipitation kinetics in alloys during thermal aging and/or under irradiation in nuclear reactors. The first part focused on developing a method to predict the thermodynamic properties of critical nuclei such as the sizes and concentration profiles of critical nuclei, and nucleation barrier. These properties are crucial for quantitative simulations of precipitate evolution kinetics with phase field models. Fe-Cr alloy was chosen as a model alloy because it has valid thermodynamic and kinetic data as well as it is an important structural material in nuclear reactors. A constrained shrinking dimer dynamics (CSDD) method was developed to search for the energy minimum path during nucleation. With the method we are able to predict the concentration profiles of the critical nuclei of Cr-rich precipitates and nucleation energy barriers. Simulations showed that Cr concentration distribution in the critical nucleus strongly depends on the overall Cr concentration as well as temperature. The Cr concentration inside the critical nucleus is much smaller than the equilibrium concentration calculated by the equilibrium phase diagram. This implies that a non-classical nucleation theory should be used to deal with the nucleation of Cr precipitates in Fe-Cr alloys. The growth kinetics of both classical and non-classical nuclei was investigated by the phase field approach. A number of interesting phenomena were observed from the simulations: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrated that it is critical to introduce the correct critical nuclei into phase field modeling in order to correctly capture the kinetics of precipitation. In most alloys the matrix phase and precipitate phase have different concentrations as well as different crystal structures. For example, Cu precipitates in FeCu alloys have fcc crystal structure while the matrix Fe-Cu solid solution has bcc structure at low temperature. The WBM model and KimS model, where both concentrations and order parameters are chosen to describe the microstructures, are commonly used to model precipitations in such alloys. The WBM and KimS models have not been implemented into Marmot yet. In the second part of this report, we focused on implementing the WBM and KimS models into Marmot. The Fe-Cu alloys, which are important structure materials in nuclear reactors, was taken as the model alloys to test the models.

Li, Yulan; Hu, Shenyang Y.; Sun, Xin

2013-09-30

91

Characterization of early stage intermediates in the nucleation phase of A? aggregation.  

PubMed

Alzheimer's disease (AD) is a common form of dementia, which is characterized by the presence of extracellular amyloid plaques comprising the amyloid ? peptide (A?). Although the mechanism underlying AD pathogenesis remains elusive, accumulating evidence suggests that the process of amyloid fibril formation is a surface-mediated event, which plays an important role in AD onset and progression. In this study, the mechanism of A? aggregation on hydrophobic surfaces was investigated with dual polarization interferometry (DPI), which provides real-time information on early stages of the aggregation process. Aggregation was monitored on a hydrophobic C18 surface and a polar silicon oxynitride surface. The DPI results showed a characteristic A? aggregation pattern involving a decrease in the density of A? at the surface followed by an increase in the thickness on the hydrophobic C18 chip. Most importantly, the DPI measurements provided unique information on the early stages of A? aggregation, which is characterized by the presence of initially slow nucleus formation process followed by exponential fibril elongation. The dimensions of the putative nucleus corresponded to a thickness of ?5 nm for both A?40 and A?42, which may represent about 10-15 molecules. The results thus support the nucleation-dependent polymerization model as indicated by the presence of a nucleation phase followed by an exponential growth phase. These results are the first reported measurements of the real-time changes in A? molecular structure during the early stages of amyloid formation at the nanometer level. PMID:22283417

Zhai, Jiali; Lee, Tzong-Hsien; Small, David H; Aguilar, Marie-Isabel

2012-02-14

92

Phase-field simulation of irradiated metals Part II : Gas bubble kinetics.  

SciTech Connect

The phase-field model developed in Part I of this work is expanded to include fission gas generation, diffusion, and segregation within bubbles nucleated both homogeneously and heterogeneously along grain boundaries. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of the irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy and bubble density are investigated.

Millett, P. C.; El-Azab, A.; Wolf, D. (Materials Science Division); (INL); (Florida State Univ.)

2011-01-01

93

The effect of magma flow on nucleation of gas bubbles in a volcanic conduit  

Microsoft Academic Search

We solve the dynamics of magma ascent and the kinetics of bubble nucleation and growth simultaneously, which allow us to predict bubble sizes and number densities under ascent conditions. As magma rises toward the surface, the pressure decreases and eventually becomes less than the solubility pressure. When the degree of supersaturation becomes great enough, bubbles nucleate. Nucleation will stop as

Hélène Massol; Takehiro Koyaguchi

2005-01-01

94

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

2002-01-01

95

Cluster nucleation and growth from a highly supersaturated adatom phase: silver on magnetite.  

PubMed

The atomic-scale mechanisms underlying the growth of Ag on the (?2×?2)R45°-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K. Above 0.5 ML, Ag clusters nucleate spontaneously and grow at the expense of the surrounding material with mild annealing. This unusual behavior results from a kinetic barrier associated with the (?2×?2)R45° reconstruction, which prevents adatoms from transitioning to the thermodynamically favorable 3D phase. The barrier is identified as the large separation between stable adsorption sites, which prevents homogeneous cluster nucleation and the instability of the Ag dimer against decay to two adatoms. Since the system is dominated by kinetics as long as the (?2×?2)R45° reconstruction exists, the growth is not well described by the traditional growth modes. It can be understood, however, as the result of supersaturation within an adsorption template system. PMID:24945923

Bliem, Roland; Kosak, Rukan; Perneczky, Lukas; Novotny, Zbynek; Gamba, Oscar; Fobes, David; Mao, Zhiqiang; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S

2014-07-22

96

Cluster Nucleation and Growth from a Highly Supersaturated Adatom Phase: Silver on Magnetite  

PubMed Central

The atomic-scale mechanisms underlying the growth of Ag on the (?2×?2)R45°-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K. Above 0.5 ML, Ag clusters nucleate spontaneously and grow at the expense of the surrounding material with mild annealing. This unusual behavior results from a kinetic barrier associated with the (?2×?2)R45° reconstruction, which prevents adatoms from transitioning to the thermodynamically favorable 3D phase. The barrier is identified as the large separation between stable adsorption sites, which prevents homogeneous cluster nucleation and the instability of the Ag dimer against decay to two adatoms. Since the system is dominated by kinetics as long as the (?2×?2)R45° reconstruction exists, the growth is not well described by the traditional growth modes. It can be understood, however, as the result of supersaturation within an adsorption template system.

2014-01-01

97

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys  

NASA Technical Reports Server (NTRS)

From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase, and the i-phase, that nucleate directly from the undercooled liquid. The reduced undercooling decreases progressively with increasing polytetrahedral order in the solid, supporting Frank s hypothesis. A new facility for direct measurements of the structures and phase transitions in undercooled liquids (BESL) was developed and has provided direct proof of the primary nucleation of a metastable icosahedral phase in some Ti-Zr-Ni alloys. The first measurements of specific heat and viscosity in the undercooled liquid of this alloy system have been completed. Other than the importance of thermo-physical properties for modeling nucleation and growth processes in these materials, these studies have also revealed some interesting new results (such as a maximum of C(sup q, sub p) in the undercooled state). These ground-based results have clearly established the necessary background and the need for conducting benchmark nucleation experiments at the ISS on this alloy system.

Kelton, K. F.; Gangopadhyay, Anup K.; Lee, G. W.; Hyers, Robert W.; Rathz, T. J.; Robinson, Michael B.; Rogers, Jan R.

2003-01-01

98

Electroweak phase transition nucleation with the MSSM and electromagnetic field creation  

SciTech Connect

Using EW-MSSM field theory, so the electroweak phase transition (EWPT) is first order, we derive the equations of motion (e.o.m.) for the gauge fields. With an isospin ansatz we derive e.o.m. for the electrically charged W fields uncoupled from all other fields. These and the lepton currents serve as the current for the Maxwell-like e.o.m. for the electromagnetic field. The electromagnetic field arising during EWPT bubble nucleation without leptons is found. We then calculate the electron current contribution, which is seen to be quite large. This provides the basis for determining the magnetic field created by EWPT bubble collisions, which could seed galactic and extragalactic magnetic fields.

Henley, Ernest M.; Johnson, Mikkel B.; Kisslinger, Leonard S. [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

2010-04-15

99

An Effective Continuum Model for the Liquid-to-Gas Phase Change in a Porous Medium Driven by Solute Diffusion: II. Constant Liquid Withdrawal Rates  

SciTech Connect

This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk gas flow, nucleation and gas phase growth. Because of negligible gradients due to gravity or viscous forces, the critical gas saturation, is only a function of the nucleation fraction.

Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.

2001-08-15

100

Distinct Nucleation and Propagation Phases of Northern Cascadia Episodic Tremor and Slip Events  

NASA Astrophysics Data System (ADS)

Northern Cascadia episodic tremor and slip (ETS) events appear to have distinct nucleation and propagation phases. We find that there is a roughly linear increase in tremor amplitude over the first ~5 days of each ETS event. We observe a corresponding linear increase in the areal distribution of tremor. These episodes typically initiate down dip, and after approximately 5 days have organized and migrated to fill the up-dip/down-dip width of the tremorgenic zone. After this time, tremor amplitudes vary wildly, modulated by tidal stresses, as the tremor propagates along strike in one or both directions at roughly 8 km/day, continuing for 4-5 weeks. Inter-ETS tremor swarms can begin similarly to ETS events, but do not reach the maximum area and amplitude of ETS events, and instead die away in less than 5-10 days. Since the increase in tremor amplitude during the nucleation phase is proportional to the increase in tremoring area, the source amplitude per unit area is approximately constant, indicating a constant radiated energy rate per unit area associated with tremor. In order to estimate tremor amplitude we use three-component seismograms from temporary deployments and permanent stations (Array of Arrays, CAFE, PNSN, TA) to estimate the amplitude of tremor bursts at the source location, using a method similar to Maeda and Obara (JGR, 2009). Source amplitude, or radiated energy rate, is proportional to the root-mean square of band limited (1.5-5.5 Hz) ground velocity for each 5-minute window. Station ground velocities and tremor locations, determined by a waveform envelope cross-correlation method (Wech and Creager, GRL, 2008), are inverted to obtain source amplitude and station statics, taking into account geometrical spreading and attenuation. The result is a catalog of source amplitudes for each of 40,000 tremor locations in northern Cascadia from 2006 to 2011.

Ulberg, C.; Creager, K. C.

2013-12-01

101

Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D.  

PubMed

We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model. PMID:21386517

Tóth, Gyula I; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László

2010-09-15

102

Kinetics of solid hydrate formation by carbon dioxide: Phase field theory of hydrate nucleation and magnetic resonance imagingy  

Microsoft Academic Search

In the course of developing a general kinetic model of hydrate formation\\/reaction that can be used to establish\\/ optimize technologies for the exploitation of hydrate reservoirs, two aspects of CO2 hydrate formation have been studied. (i) We developed a phase field theory for describing the nucleation of CO2 hydrate in aqueous solutions. The accuracy of the model has been demonstrated

B. Kvamme; A. Graue; T. Kuznetsova; L. Granasy; G. Toth; T. Pusztaib; G. Tegzeb

2004-01-01

103

Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.

Kelton, K. F.; Croat, T. K.; Gangopadhyay, A.; Holland-Moritz, D.; Hyers, Robert W.; Rathz, Thomas J.; Robinson, Michael B.; Rogers, Jan R.

2001-01-01

104

PHASE-FIELD SIMULATION OF IRRADIATED METALS: PART II: GAS BUBBLE KINETICS  

SciTech Connect

We present a phase-field model for inert gas bubble formation and evolution in irradiated metals. The model evolves vacancy, self-interstitial, and fission gas atoms through a coupled set of Cahn-Hilliard and Allen-Cahn equations, capturing the processes of defect generation, recombination, annihilation at GB sinks, as well as intragranular and intergranular bubble nucleation and growth in polycrystalline microstructures. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of varying irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy on GB motion, and bubble density are investigated.

Paul C Millett; Anter El-Azab

2011-01-01

105

Nucleation stage with nonsteady growth of supercritical gas bubbles in a strongly supersaturated liquid solution and the effect of excluded volume  

Microsoft Academic Search

An approach to the kinetics of barrier formation of supercritical gas bubbles in a strongly supersaturated liquid solution is presented. A common assumption of uniform reduction of a dissolved gas supersaturation in a liquid solution via stationary diffusion to nucleating gas bubbles is shown to be not applicable to the case of high gas supersaturations. The approach recognizes that the

Anatoly E. Kuchma; Fedor M. Kuni; Alexander K. Shchekin

2009-01-01

106

Distribution of density fluctuations in a molecular theory of vapor-phase nucleation  

NASA Astrophysics Data System (ADS)

A statistical-mechanical theory of the distribution of density fluctuations involved in homogeneous vapor-phase nucleation is presented which improves on previous work. Specifically, a refined characterization of a physical cluster is developed. This cluster is known as an i/v cluster, since it is defined by both a molecular number i and a volume v (i/v is the average density of molecules in the cluster). The i/v cluster represents the density fluctuations that have the potential to serve as condensation centers for the formation of liquid drops. The refinement involves a so-called shell molecule which defines the volume v. The equilibrium distribution of the refined i/v clusters is derived, using an approach involving fluctuation theory. This method is as rigorous as prior approaches and, moreover, sheds light on the nature of the cluster distribution and the cluster itself. Through an analysis of a cluster defined without a shell molecule, it is shown that the shell molecule is necessary if the cluster characterization is to be consistent with the fundamental statistical-mechanical description of the supersaturated vapor. Finally, as a by-product of this work, it is shown that the awkwardness of the constant-pressure ensemble associated with its expression as a sum over volume is automatically removed once the necessary presence of a shell molecule is recognized.

Ellerby, H. Michael

1994-05-01

107

Thermodynamics and nucleation studies of III-nitride materials grown from vapor phase  

NASA Astrophysics Data System (ADS)

The initial stage of growth of III-Nitrides ternary compound on binary substrate were analyzed using the classical heterogeneous nucleation theory, incorporating lattice mismatch between the grown alloy and the substrate. The explicit expression for the lattice mismatch induced supercooling for the growth of the chosen system was established, and it was used to evaluate the nucleation parameters. It has been theoretically shown that the nucleation barrier for the formation of ternary alloy on binary substrate depends on the composition of the alloy. .

Varadarajan, E.; Dhanasekaran, R.; Ramasamy, P.

2000-08-01

108

Transient nucleation in glasses  

NASA Technical Reports Server (NTRS)

Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

Kelton, K. F.

1991-01-01

109

Phase-field simulations of gas density within bubbles under irradiation  

SciTech Connect

Phase-field simulations are used to study the evolution of gas density within irradiation-induced bubbles. In our simulations, the dpa rate, gas production rate, and defect diffusivities are systematically varied to understand their effect on bubble nucleation rates, bubble densities, and the distribution of gas concentration within bubbles and in the solid regions. We find that gas densities within bubbles fluctuate drastically in the early nucleation stages, when growth rates are highest, but converge to steady-state values during the later coarsening stages. The steady-state gas densities within bubbles correspond with the ratio of total accumulated vacancy content divided by the total accumulated gas content, in agreement with a thermodynamic analysis concerning free-energy minimization.

Paul C. Millett; Anter El-Azab; Michael Tonks

2011-05-01

110

A Refined Approach to Bubble Nucleation and Polymer Foaming Process: Dissolved Gas and Cluster Size Effects  

Microsoft Academic Search

A refined approach to bubble nucleation is presented and applied to polymer foaming process. The integral overall energy balance and the integral Clausius-Duhem inequality are used to analyze a bubble nucleation experiment. The computation of long-range intermolecular potential results in expressions for surface tension, work, and critical work for cluster formation, as functions of the Hamaker constant, molecular and\\/or repeat

James G. Lee; Raymond W. Flumerfelt

1996-01-01

111

Influence of ferrite nanoparticle type and content on the crystallization kinetics and electroactive phase nucleation of poly(vinylidene fluoride).  

PubMed

This work reports on the nucleation of the ?-phase of poly(vinylidene fluoride) (PVDF) by incorporating CoFe(2)O(4) and NiFe(2)O(4) nanoparticles, leading in this way to the preparation of magnetoelectric composites. The fraction of filler nanoparticles needed to produce the same ?- to ?-phase ratio in crystallized PVDF is 1 order of magnitude lower in the cobalt ferrite nanoparticles. The interaction between nanoparticles and PVDF chains induce the all-trans conformation in PVDF segments, and this structure then propagates in crystal growth. The nucleation kinetics is enhanced by the presence of nanoparticles, as corroborated by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avrami's exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticle content indicates that an important fraction of polymer chains are confined in interphases with the filler particle. PMID:21545124

Sencadas, Vitor; Martins, Pedro; Pitães, Alexandre; Benelmekki, Maria; Gómez Ribelles, José Luis; Lanceros-Mendez, Senentxu

2011-06-01

112

Nucleation, Drift, and Decay of Phase Bubbles in Period-2 Oscillatory Wave Trains in a Reaction-Diffusion System  

NASA Astrophysics Data System (ADS)

This is a report on experimental observations of phase bubbles, simply closed boundaries between domains oscillating 2? out of phase, associated with period-2 oscillatory traveling waves in a Belousov-Zhabotinsky reaction-diffusion system. The bubbles nucleate spontaneously through a fast localized phase slip, drift radially away from a neighboring spiral wave core in an oscillatory fashion, and gradually shrink to disappear. Their oscillatory drift along the radial direction is a consequence of “period adaptation,” while their lateral shrinkage is an attribute of local curvature. Similar dynamic structures can be reproduced in a simple, three-species reaction-diffusion model that supports period-2 oscillatory wave trains.

Park, Jin-Sung; Woo, Sung-Jae; Kwon, Okyu; Kim, Tae Yun; Lee, Kyoung J.

2008-02-01

113

Formation of Single-Magnetic-Domain Iron Particles via Vapor-Phase Nucleation: Implications for the Solar Nebula  

Microsoft Academic Search

We report experimental evidence of the production of single-magnetic-domain iron grains via vapor-phase nucleation even in the absence of an ambient magnetic field. These single domain grains are thermodynamically stable as fully saturated magnetic dipoles. The spontaneous formation of fully magnetized single-domain iron grains, and by inference a variety of other single-domain particles such as taenite or magnetite, could greatly

Paul A. Withey; Joseph A. Nuth

1999-01-01

114

Nucleation and amorphization of radiation-produced phases in a modified austenitic stainless steel during Ni-ion irradiation  

SciTech Connect

The nucleation and amorphization of radiation-induced (G) and radiation-enhanced (eta) phases in a silicon- and titanium-modified austenitic stainless steel have been studied under nickel-ion irradiation. These silicon- and nickel-enriched phases form under high-temperature (950 K) irradiation as the result of radiation-induced segregation to radiation-produced interstitial dislocation loops. Availability of carbon promotes the formation of eta phase relative to G phase. Under lower temperature (450 K) irradiation, G and eta phases are amorphized without significant change in composition of metallic elements. Two carbide phases (MC, M/sub 23/C/sub 6/) remain crystalline for the same irradiation conditions. The amorphization of the silicides may result from (1) radiation damage increasing their free energy above that of the amorphous state or (2) direct formation of the amorphous phase in the damage cascade.

Lee, E.H.; Kenik, E.A.

1988-09-01

115

Comment on"Elucidating the Mechanism of Nucleation near the Gas-Liquid Spinodal"  

SciTech Connect

In a recent Letter [1], Bhimalapuram, Chakrabarty and Bagchi (BCB) study the phase transformation mechanism of the Lennard-Jones fluid and the non-conserved Ising model. They compute the free energy as a function of the size of the largest droplet of the stable phase. In apparent contradiction to classical nucleation theory (CNT), they find that in both systems the free energy develops a minimum at subcritical cluster sizes. In this Comment we argue that this minimum is specific to the chosen order parameter, and that the observed behavior is in fact consistent with CNT. CNT states that the free energy F(N) of a single cluster of size N is a concave function with a maximum at the critical nucleus size N{sub c}. BCB, on the other hand, calculate the probability distribution of N*, the size of the largest cluster in the system, and compute the free energy {beta}F*(N*) = -ln P(N*), where {beta} = 1/k{sub B}T. This order parameter does not measure the size of a single cluster. Instead, when sampling small values of N*, one measures the statistical weight of configurations in which all clusters are at most N* in size. Hence a free energy penalty is incurred when one constrains N* to values smaller than the largest average cluster in the simulation volume V. It is this penalty that causes the sudden increase of F* as N* {yields} 0 and the minimum at intermediate values of N*. We now illustrate how F(N) can be calculated from simulations. Our argument is intuitive but not exact, a formal derivation that yields an equivalent result can be found in Ref. 2. We choose the Ising model for concreteness. We aim to compute the probability that a given cluster has size N, where we imagine the center of the cluster to be fixed at site i. To simplify the calculation we consider clusters that overlap with site i, and correct for the N-fold translational degeneracy in a second step.

Maibaum, Lutz; Maibaum, Lutz

2008-06-18

116

Numerical model of solid phase transformations governed by nucleation and growth: Microstructure development during isothermal crystallization  

NASA Astrophysics Data System (ADS)

A simple numerical model which calculates the kinetics of crystallization involving randomly distributed nucleation and isotropic growth is presented. The model can be applied to different thermal histories and no restrictions are imposed on the time and the temperature dependences of the nucleation and growth rates. We also develop an algorithm which evaluates the corresponding emerging grain-size distribution. The algorithm is easy to implement and particularly flexible, making it possible to simulate several experimental conditions. Its simplicity and minimal computer requirements allow high accuracy for two- and three-dimensional growth simulations. The algorithm is applied to explore the grain morphology development during isothermal treatments for several nucleation regimes. In particular, thermal nucleation, preexisting nuclei, and the combination of both nucleation mechanisms are analyzed. For the first two cases, the universal grain-size distribution is obtained. The high accuracy of the model is stated from its comparison to analytical predictions. Finally, the validity of the Kolmogorov-Johnson-Mehl-Avrami model [J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940); 9, 177 (1941); Trans. Am. Inst. Min., Metall. Pet. Eng. 135, 416 (1939); Izv. Akad. Nauk SSSR, Ser. Fiz. 1, 355 (1937)] is verified for all the cases studied.

Farjas, Jordi; Roura, Pere

2007-05-01

117

A Refined Approach to Bubble Nucleation and Polymer Foaming Process: Dissolved Gas and Cluster Size Effects  

PubMed

A refined approach to bubble nucleation is presented and applied to polymer foaming process. The integral overall energy balance and the integral Clausius-Duhem inequality are used to analyze a bubble nucleation experiment. The computation of long-range intermolecular potential results in expressions for surface tension, work, and critical work for cluster formation, as functions of the Hamaker constant, molecular and/or repeat unit interaction distance, molar fractions of each component, and cluster radius. The variation of surface tension with cluster size, temperature, and pressure is determined in terms of well-known macroscopic properties and compared with available experimental data. PMID:8978536

Lee; Flumerfelt

1996-12-25

118

Effect of noise-induced nucleation on grain size distribution studied via the phase-field crystal method  

NASA Astrophysics Data System (ADS)

We contribute to the more detailed understanding of the phase-field crystal model recently developed by Elder et al (2002 Phys. Rev. Lett. 88 245701), by focusing on its noise term and examining its impact on the nucleation rate in a homogeneously solidifying system as well as on successively developing grain size distributions. In this context we show that principally the grain size decreases with increasing noise amplitude, resulting in both a smaller average grain size and a decreased maximum grain size. Despite this general tendency, which we interpret based on Panfilis and Filiponi (2000 J. Appl. Phys. 88 562), we can identify two different regimes in which nucleation and successive initial growth are governed by quite different mechanisms.

Hubert, J.; Cheng, M.; Emmerich, H.

2009-11-01

119

Nucleation kinetics of a solid phase in supercooled melts or liquids under heat-insulating conditions (The Initial Stage)  

NASA Astrophysics Data System (ADS)

The initial stage of decomposition of a supercooled melt or a viscous liquid under heat-insulating conditions has been considered in terms of the method of virtual media. The heat removal from the interface is taken as the controlling process in the vicinity of a growing nucleus. In addition to the quasi-steady-state equations (which already became standard) for the nucleation rate and the distribution function of subcritical particles of a new phase, an estimating equation has been derived for the time required to reach steady-state values of these characteristics. Numerical evaluations have been performed for nickel. It has been demonstrated that the chosen model of the controlling process is valid only under the condition of weak heat removal. Attention has been drawn to the difference between the "diffusion" and "thermal" processes of nucleation.

Slezov, V. V.; Ostapchuk, P. N.

2011-03-01

120

Coupled effects of magma flow and nucleation of gas bubbles in a volcanic conduit  

Microsoft Academic Search

We solve the dynamics of magma ascent and the kinetics of bubble nucleation and growth simultaneously, which allow us to predict bubble sizes and number density under ascent conditions. As magma rises toward the surface the pressure decreases and eventually becomes less than the solubility pressure. When the difference between the concentration of volatiles in the melt and the concentration

H. Massol; T. Koyaguchi

2003-01-01

121

Nucleation stage with nonsteady growth of supercritical gas bubbles in a strongly supersaturated liquid solution and the effect of excluded volume.  

PubMed

An approach to the kinetics of barrier formation of supercritical gas bubbles in a strongly supersaturated liquid solution is presented. A common assumption of uniform reduction of a dissolved gas supersaturation in a liquid solution via stationary diffusion to nucleating gas bubbles is shown to be not applicable to the case of high gas supersaturations. The approach recognizes that the diffusion growth of supercritical bubbles at high gas supersaturation is essentially nonstationary. Nonstationary growth of an individual gas bubble is described by a self-similar solution of the diffusion equation which predicts a renormalized growth rate and thin highly nonuniform diffusion layer around the bubble. The depletion of a dissolved gas due to intake of gas molecules by the bubble occurs only within this thin layer. An integral equation for the total volume of an ensemble of supercritical gas bubbles within a liquid solution is derived. This equation describes the effect of excluding a total volume of the depleted diffusion layers around the growing bubbles nucleated at all previous moments of time until nucleation of new bubbles ceases due to elimination of the nondepleted volume of the solution. An analytical solution of this equation is found. The swelling of the liquid solution, the number of gas bubbles nucleated, the distribution function of bubbles in their sizes, and the mean radius of the bubbles are determined in their dependence on time. PMID:20365136

Kuchma, Anatoly E; Kuni, Fedor M; Shchekin, Alexander K

2009-12-01

122

Rate processes in gas phase  

NASA Technical Reports Server (NTRS)

Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

Hansen, C. F.

1983-01-01

123

Nucleation of a stable solid from melt in the presence of multiple metastable intermediate phases: wetting, Ostwald's step rule, and vanishing polymorphs.  

PubMed

In many systems, nucleation of a stable solid may occur in the presence of other (often more than one) metastable phases. These may be polymorphic solids or even liquid phases. Sometimes, the metastable phase might have a lower free energy minimum than the liquid but higher than the stable-solid-phase minimum and have characteristics in between the parent liquid and the globally stable solid phase. In such cases, nucleation of the solid phase from the melt may be facilitated by the metastable phase because the latter can "wet" the interface between the parent and the daughter phases, even though there may be no signature of the existence of metastable phase in the thermodynamic properties of the parent liquid and the stable solid phase. Straightforward application of classical nucleation theory (CNT) is flawed here as it overestimates the nucleation barrier because surface tension is overestimated (by neglecting the metastable phases of intermediate order) while the thermodynamic free energy gap between daughter and parent phases remains unchanged. In this work, we discuss a density functional theory (DFT)-based statistical mechanical approach to explore and quantify such facilitation. We construct a simple order-parameter-dependent free energy surface that we then use in DFT to calculate (i) the order parameter profile, (ii) the overall nucleation free energy barrier, and (iii) the surface tension between the parent liquid and the metastable solid and also parent liquid and stable solid phases. The theory indeed finds that the nucleation free energy barrier can decrease significantly in the presence of wetting. This approach can provide a microscopic explanation of the Ostwald step rule and the well-known phenomenon of "disappearing polymorphs" that depends on temperature and other thermodynamic conditions. Theory reveals a diverse scenario for phase transformation kinetics, some of which may be explored via modern nanoscopic synthetic methods. PMID:23713546

Santra, Mantu; Singh, Rakesh S; Bagchi, Biman

2013-10-24

124

Nucleation of lamellar domains from a sponge phase under shear flow: Shape selection of nuclei in a nonequilibrium steady state.  

PubMed

It is a fundamental physical problem how a state is selected in a nonequilibrium steady state where the energy is continuously dissipated. This problem is common to phase transitions in liquids under shear flow and those in solids under deformation or electric current. In particular, soft matter often exhibits a strong nonlinear response to an external field, since its structural susceptibility to the external field is extremely large due to its softness and flexibility. Here we study the nucleation and growth process of the lamellar phase from the sponge phase under shear flow in a bilayer-forming surfactant system. We found an interesting shape selection of lamellar nuclei under shear flow between multilamellar vesicles (onions) and cylinders (leeks). These two types of behavior are separated sharply at a critical shear rate: a slight change of the shear rate is enough to switch one behavior to the other. We also found that, under a sufficiently strong shear flow, nucleated onions decrease their size with time, and eventually transform into leeks. This suggests that leeks may be the stable morphology under steady shear flow. However, the stability is limited only to the lamellar-sponge coexistence region. When a system enters into the lamellar phase region by further cooling, leeks lose their stability and break up into rather monodisperse onions, presumably via Rayleigh-like instability of a fluid tube. On the basis of these results, we draw a dynamic state diagram of smectic membrane organization under shear flow. PMID:17677456

Miyazawa, Hideyuki; Tanaka, Hajime

2007-07-01

125

Nucleation of lamellar domains from a sponge phase under shear flow: Shape selection of nuclei in a nonequilibrium steady state  

NASA Astrophysics Data System (ADS)

It is a fundamental physical problem how a state is selected in a nonequilibrium steady state where the energy is continuously dissipated. This problem is common to phase transitions in liquids under shear flow and those in solids under deformation or electric current. In particular, soft matter often exhibits a strong nonlinear response to an external field, since its structural susceptibility to the external field is extremely large due to its softness and flexibility. Here we study the nucleation and growth process of the lamellar phase from the sponge phase under shear flow in a bilayer-forming surfactant system. We found an interesting shape selection of lamellar nuclei under shear flow between multilamellar vesicles (onions) and cylinders (leeks). These two types of behavior are separated sharply at a critical shear rate: a slight change of the shear rate is enough to switch one behavior to the other. We also found that, under a sufficiently strong shear flow, nucleated onions decrease their size with time, and eventually transform into leeks. This suggests that leeks may be the stable morphology under steady shear flow. However, the stability is limited only to the lamellar-sponge coexistence region. When a system enters into the lamellar phase region by further cooling, leeks lose their stability and break up into rather monodisperse onions, presumably via Rayleigh-like instability of a fluid tube. On the basis of these results, we draw a dynamic state diagram of smectic membrane organization under shear flow.

Miyazawa, Hideyuki; Tanaka, Hajime

2007-07-01

126

Ion irradiation-induced phase transformations in bixbyite-fluorite related oxides: The role of dislocation loop nucleation  

NASA Astrophysics Data System (ADS)

The ion irradiation induced phase transformations of bixbyite-fluorite related oxides have been studied with thin films of Y2O3 grown on Si and SrTiO3 by an ion beam sputtering technique which allows to control the microstructure and stresses within the film. Y2O3 thin films are ion-irradiated with an xenon beam in an energy range 60-380 keV at a fluence of 4.4 × 1015 Xe/cm2 at 80 K. Depending on the energy of the xenon beam two different structural phase transformations are observed: cubic to nanocrystalline/amorphous and cubic to monoclinic phase transformations. The phase transformation are analysed in terms of structural extended defect nucleation like prismatic dislocation loops due to the oxygen network behaviour under ion irradiation.

Gaboriaud, Rolly J.; Lacroix, Bertrand; Paumier, Fabien

2012-04-01

127

Phase equilibria in natural gas systems  

Microsoft Academic Search

Previously unavailable information on the phase equilibria of helium-bearing natural gas is presented. The solubility of helium in the equilibrium liquid phases, the percentage of helium condensed, and equilibrium coefficient data for methane, nitrogen, and helium are considered.

L. W. Brandt; L. Stroud; J. E. Miller

1961-01-01

128

High-speed rewritable DVD up to 20 m\\/s with nucleation-free eutectic phase-change material of Ge(Sb70Te30)+Sb  

Microsoft Academic Search

High speed overwriting capability of the nucleation-free and growth-dominant eutectic Ge(Sb70Te30)+Sb phase- change material, and its application to high speed overwritable DVD and CD, are discussed. The addition of Ge to Sb70Te30+Sb binary system could effectively suppress the nucleation in recrystallization process, while high Sb\\/Te ratio could realize a selective enhancement of crystalline growth-speed initiated from the boundary of an

Michikazu Horie; Natsuko Nobukuni; Kenjiro Kiyono; Takashi Ohno

2000-01-01

129

Gas phase kinetics during normal combustion  

NASA Technical Reports Server (NTRS)

The role of gas phase kinetics during combustion was explored in the steady state modeling efforts and in the analysis of ignition phenomena. In both cases it was shown that the combustion characteristics of some high energy ingredients and propellants are strongly affected, if not dictated, by the gas phase reactions which take place.

Price, C. F.; Boggs, T. L.; Eisel, J. L.; Atwood, A. I.; Zurn, D. E.

1980-01-01

130

Solubility of aqueous methane under metastable conditions: implications for gas hydrate nucleation.  

PubMed

To understand the prenucleation stage of methane hydrate formation, we measured methane solubility under metastable conditions using molecular dynamics simulations. Three factors that influence solubility are considered: temperature, pressure, and the strength of the modeled van der Waals attraction between methane and water. Moreover, the naturally formed water cages and methane clusters in the methane solutions are analyzed. We find that both lowering the temperature and increasing the pressure increase methane solubility, but lowering the temperature is more effective than increasing the pressure in promoting hydrate nucleation because the former induces more water cages to form while the latter makes them less prevalent. With an increase in methane solubility, the chance of forming large methane clusters increases, with the distribution of cluster sizes being exponential. The critical solubility, beyond which the metastable solutions spontaneously form hydrate, is estimated to be ~0.05 mole fraction in this work, corresponding to the concentration of 1.7 methane molecules/nm(3). This value agrees well with the cage adsorption hypothesis of hydrate nucleation. PMID:23639139

Guo, Guang-Jun; Rodger, P Mark

2013-05-30

131

Phase-field Modeling of Gas Bubbles and Thermal Conductivity Evolution in Nuclear Fuels  

SciTech Connect

The major factors that influence the thermal conductivity of the ceramics and metals are temperature, stoichiometry, microstructure, porosity, and point defects. Nuclear fuels and structure materials are subject to a severe radiation environment and their properties, including thermal conductivity change significantly with time and irradiation level. In particular, the accumulation of fission products and the formation of He bubbles can decrease the heat transfer, leading to overheating of the fuel element. In this work, we use the phase-field method to study the effect of microstructural changes on thermal conductivity. We developed a phase-field model to simulate the He bubble formation and growth in a single/polycrystalline material with defects. The model takes into account the generation of gas atoms and defects, gas atom diffusivity inhomogeneity, gas atom segregation, and gas bubble nucleation. With the model, we simulated the gas bubble and temperature evolution, and calculated the effect of gas bubble volume fraction on effective thermal conductivity.

Hu, Shenyang Y.; Henager, Charles H.; Heinisch, Howard L.; Stan, Marius; Baskes, Michael I.; Valone, Steven

2009-07-15

132

Aerosol flow in a tube furnace reactor of gas-phase synthesised silver nanoparticles  

Microsoft Academic Search

In a previous work, gas-phase synthesis of silver nanoparticles through evaporation of silver powder and subsequent particle\\u000a nucleation by cooling was shown to be a viable method for achieving high purity silver nanoparticles (Backman et al. J Nanopart\\u000a Res 4:325–335, 2002). In order to control the size of the produced nanoparticles, careful design of the reactor is required with respect

D. Mitrakos; J. Jokiniemi; U. Backman; C. Housiadas

2008-01-01

133

Solvable lattice gas models with three phases  

NASA Astrophysics Data System (ADS)

Phase boundaries in p-T and p-V diagrams are essential in material science researches. Exact analytic knowledge about such phase boundaries are known so far only in two-dimensional (2D) Ising-like models, and only for cases with two phases. In the present paper we present several lattice gas models, some with three phases. The phase boundaries are either analytically calculated or exactly evaluated.

Wei, B. B.; Yang, C. N.

2013-06-01

134

The stability of bubbles formed from supersaturated solutions, and homogeneous nucleation of gas bubbles from solution, both revisited.  

PubMed

The solution of the problem of the relative stability of all possible equilibrium bubble states that can form from a closed, finite, supersaturated gas-liquid solution, maintained at a fixed temperature and a fixed external pressure is given. The supersaturated solution may contain any number of dissolved volatile solutes. The full solution to this problem has remained elusive for decades, because of the complication of pressure inequalities between the bubbles and the constant external (or reservoir) pressure. The method of solution is one that had been used previously to solve the related problem of the stability of a liquid droplet in a supersaturated vapor, where the same complication occurred. The derived equations were found to reduce correctly when simplified; they were consistent with experiment, and the system Gibbs free energy appropriately obeyed the Law of Corresponding States. The expressions were used in the context of transition state theory to provide semiempirical predictions of the rate of homogeneous bubble formation from a supersaturated solution, and the "critical pressure for homogeneous nucleation (P(crit))". The nucleation Gibbs free energy expression derived here had a lower barrier height and resulted in a reduction of P(crit) values, relative to what was obtained from the basis of a pre-existing approximate expression taken from the literature. Applications to chemical engineering and human decompression modeling are briefly described. PMID:19032116

Goldman, Saul

2008-12-25

135

Effect of point defect interaction with bubble surface on the nucleation and growth of gas bubbles  

Microsoft Academic Search

The influence of absorption ability of gas bubble surface on bubble kinetics in supersaturated solid solution of vacancies self-interstitial and gas atoms is investigated. Depending on the peculiarities of point defect absorption\\/desorption at the bubble surface possible cases of gas bubble ensemble kinetics are described.

Roman E. Voskoboinikov; Alexander E. Volkov

2001-01-01

136

Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation  

NASA Technical Reports Server (NTRS)

The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets appear inside the gas mixture due to a uniform nucleation and the temperature recovers, thus the motion of the bubble is apparently isothermal; (2) the evaporation and condensation coefficient largely affects bubble motions (maximum radius, period and rate of attenuation of the bubble oscillation) including the uniform contraction; (3) the oscillation period of the bubble is longer as the equilibrium bubble radius is larger when the surrounding pressure decreases stepwise. In this circumstance the temperature inside the bubble is kept constant due to condensation evaporation phenomena and is nearly isothermal; and (4) when the surrounding pressure decreases in a stepwise fashion, the critical pressure bubble radius relation becomes closer to that for the isothermal process if the bubble radius is larger than 8 microns.

Matsumoto, Y.

1988-01-01

137

Atmospheric nucleation: Measurements, mechanisms, and dynamics  

NASA Astrophysics Data System (ADS)

New particle formation by nucleation of gas-phase species significantly influences the size distributions and number concentrations of atmospheric aerosols. These nucleated particles are formed at rates that are orders of magnitude higher than were predicted by early models and grow at rates that are typically ten times faster than can be explained by the condensation of sulfuric acid alone. The resultant aerosols exert a significant impact on global climate by affecting the earth's radiation balance directly through the scattering and absorption of incident solar radiation, and indirectly through their role as cloud condensation nuclei (CCN). High formation rates and fast growth to CCN sizes ensure that NPF contributes significantly to the global CCN population. It is the primary goal of the research described in this thesis to develop robust models, constrained by measurement, for the sequential formation of CCN from the nucleation of gas-phase precursors. To this end, my thesis focuses on four topics: the development of nucleation rate parameterizations from correlations between formation rates of 1 nm particles and gas-phase sulfuric acid concentrations in diverse environments; the development of a cluster formation mechanism incorporating energetic barriers at the smallest clusters; the derivation of a simple, dimensionless criterion determining whether or not NPF would occur on a particular day; and the determination of the survival probability of newly formed particles (3 nm) as they grow to a CCN-active size (100 nm).

Kuang, Chongai

138

Gas Phase Analysis of Diamond Growth Chemical Vapor Deposition Systems.  

NASA Astrophysics Data System (ADS)

The gas composition of two diamond film chemical vapor deposition (CVD) systems is probed with absorption spectroscopy. The gas temperature in a hot filament diamond CVD system is derived from the vacuum ultraviolet absorption spectrum of the H_2 molecule using synchrotron continuum radiation. The gas temperature is influenced most strongly by the substrate temperature, less strongly by heat conduction from the filament, and is nearly unaffected by heat deposited or absorbed by chemical reactions. The density of methyl radicals (CH _3) and the mole fraction of acetylene are measured in a hot filament CVD system both during and after an initial pretreatment that is intended to enhance the crystal nucleation density. The measurements suggest that the surface condition of the filament is the primary factor affecting the gas phase chemistry both during and after the pretreatment. The densities of CH_3 and CH and the hydrogen dissociation fraction are measured in a hot filament diamond CVD system for each of five different hydrocarbon input gases. The crystal growth rate and morphology of the diamond grown from the different input gases are also examined. The results indicate that the nature of the input hydrocarbon is relatively unimportant, and that the addition of oxygen greatly alters the gas phase chemistry and the filament surface condition. The absolute column densities of CH_3 and CH and the hydrogen dissociation ratio are measured in a DC hollow cathode plasma-assisted CVD system. The plasma gas temperature is determined using the H _2 emission spectrum near 460 nm. The CH _3 and CH densities are compared with measurements made in the hot filament CVD system.

Menningen, Kenneth Lee

1995-01-01

139

The role of vacancies and dislocations in the nucleation and growth of gas bubbles in irradiated fissile material  

Microsoft Academic Search

It is shown that fine-scale bubbles are to be expected in reasonably ; pure uranium, the bubbles nucleating either homogeneously with a spacing less ; than a micron or on any suitable nucleation sites that may exist on this or a ; finer scale. The precise value of the homogeneous nucleation spacing depends on ; the diffusion coefficient of the

G. W. Greenwood; A. J. E. Foreman; D. E. Rimmer

1959-01-01

140

Bubble nucleation dynamics in 3He\\/4He mixture by holographic interferometry  

Microsoft Academic Search

We were able to nucleate a gas bubble in the diluted phase of 3He-4He mixture by a 1 ms width strong sound pulse. The nucleated bubble became large and detached from the bottom transducer and was pushed out to the bulk liquid by the acoustic wave pulse. The bubble then repeatedly expanded and contracted a few times and finally disappeared.

M. Morikawa; H. Abe; R. Nomura; Y. Okuda

2009-01-01

141

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Technical Reports Server (NTRS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

2002-01-01

142

Gas-Phase Infrared; JCAMP Format  

National Institute of Standards and Technology Data Gateway

SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

143

Controlling the locus of bubble nucleation by dissolved gases in heterogeneous liquid-liquid systems.  

PubMed

We have examined the nucleation of chemically generated nitrogen gas bubbles in microheterogeneous systems, using optical microscopy on a model system consisting of a single liquid-liquid interface. Results clearly show that bubble nucleation occurs in both the aqueous and oil phases, despite the nitrogen production reaction being a purely aqueous phase process. A theoretical model is developed which describes the time evolution of the nitrogen concentration profile, and this reveals that bubbles in the oil are a result of homogeneous nucleation of dissolved N(2) transported across the interface into a (supersaturated) diffusion layer. We further show that bubble nucleation in the oil can be inhibited or eliminated by adding water-soluble surfactants, which facilitates aqueous phase bubble nucleation and then acts as highly effective nitrogen sinks, severely reducing the flux of dissolved gas across the water-oil interface. PMID:19754069

Priyananda, Pramith; Hawkett, Brian S; Warr, Gregory G

2010-01-19

144

Project ARGO: Gas phase formation in simulated microgravity  

NASA Technical Reports Server (NTRS)

The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

1993-01-01

145

The influence of additives and metal rods on the nucleation and growth of gas hydrates  

Microsoft Academic Search

A major technical issue in industrial applications of the gas hydrate storage process is to develop a practical means for rapid hydrate formation. In this paper, the formation processes of HCFC141b (CH3CCl2F) gas hydrate in a column of water with additives and with an iron rod that was placed in the center of the column have been studied to reveal

Jinping Li; Deqing Liang; Kaihua Guo; Ruzhu Wang

2005-01-01

146

Phase-jump nucleation in a one-dimensional model of a supersolid  

NASA Astrophysics Data System (ADS)

We consider the activation of phase jumps in a one-dimensional Bose-Einstein condensate. Our system includes a nonlocal interaction term which mimics, for example, a dipole-blockaded Rydberg system. In the mean-field limit the condensate can form superfluid droplets, arranged periodically on a line, thus displaying a supersolidlike ground state. Under an imposed velocity, phase jumps will develop. We study these phase jumps numerically and analytically, and are able to write down a relationship between the velocity, the width of the density peaks, the number of phase jumps, and ?, a parameter that determines the number of peaks in the condensate.

Mason, Peter; Josserand, Christophe

2013-12-01

147

Gravity effects in the problem of gas bubble formation and dynamics in liquid phase  

Microsoft Academic Search

Gravity effects in the problem of nucleation, development, and dynamics of gaseous inclusions in liquid phase are considered under gravity and microgravity conditions. It is shown that gravity has an impact on nucleation due to both the hydrostatic pressure in liquid and the capillary pressure. For poor wetting the latter effect suppresses the bubble nucleation with the evaporation of volatile

V. P. Shalimov

1991-01-01

148

Sigma-phase equilibria and nucleation in Fe-Cr-Ni alloys at high temperature  

Microsoft Academic Search

The sigma-phase is of crucial importance because of the disadvantageous influence on mechanical properties of the commercial alloys, mainly lowering the impact toughness and reducing creep ductility. It is usually assumed that the sigma-phase forms in the iron based alloys which contain the high level Cr and the formation is not possible above 1,104 K and below about 713 K

J. Sopoušek; T. Krurnl

1996-01-01

149

Effect of fluctuations on the surface tension of liquid droplets and gas bubbles and their nucleation  

Microsoft Academic Search

Correlations are established between the surface tension of liquid droplets and gas bubbles, and fluctuations in the volume,\\u000a density, and number of particles in their core,. The smallest droplet or bubble size below which the homogeneity of its core\\u000a starts to disturb is estimated. It is shown that, for the nuclei containing as few as several tens of microparticles (molecules

E. V. Veitsman

2007-01-01

150

Ionic liquid stationary phases for gas chromatography.  

PubMed

This article provides a summary of the development of ionic liquids as stationary phases for gas chromatography beginning with early work on packed columns that established details of the retention mechanism and established working methods to characterize selectivity differences compared with molecular stationary phases through the modern development of multi-centered cation and cross-linked ionic liquids for high-temperature applications in capillary gas chromatography. Since there are many reviews on ionic liquids dealing with all aspects of their chemical and physical properties, the emphasis in this article is placed on the role of gas chromatography played in the design of ionic liquids of low melting point, high thermal stability, high viscosity, and variable selectivity for separations. Ionic liquids provide unprecedented opportunities for extending the selectivity range and temperature-operating range of columns for gas chromatography, an area of separation science that has otherwise been almost stagnant for over a decade. PMID:21290604

Poole, Colin F; Poole, Salwa K

2011-04-01

151

On the nucleation and propagation of phase transformation fronts in a NiTi alloy  

Microsoft Academic Search

In this paper we present an experimental methodology for simultaneous full field monitoring of the deformation and thermal changes in NiTi during mechanically unstable regimes associated with the pseudoelastic material response. The deformation history is established by photographically recording surface changes of a brittle coating as austenite-martensite phase transition fronts traverse the specimen. Temperature changes are monitored by infrared thermal

J. A. Shaw; S. Kyriakides

1997-01-01

152

Nucleation mechanism of the eutectic phases in aluminum-silicon hypoeutectic alloys  

SciTech Connect

A theory is presented to explain the mechanism of formation of the eutectic phases in Al-Si hypoeutectic alloys. Results include optical, scanning and transmission electron microscopy, as well as selected area electron diffraction analysis and elemental X-ray mapping performed on Al-Si hypoeutectic alloy samples. The alloy samples had precisely controlled chemistry and were solidified at various cooling rates. The data presented support the proposed theory with microstructural and crystallographic evidence.

Shankar, Sumanth; Riddle, Yancy W.; Makhlouf, Makhlouf M

2004-09-06

153

Nucleation mechanism of the eutectic phases in aluminum–silicon hypoeutectic alloys  

Microsoft Academic Search

A theory is presented to explain the mechanism of formation of the eutectic phases in Al–Si hypoeutectic alloys. Results include optical, scanning and transmission electron microscopy, as well as selected area electron diffraction analysis and elemental X-ray mapping performed on Al–Si hypoeutectic alloy samples. The alloy samples had precisely controlled chemistry and were solidified at various cooling rates. The data

Sumanth Shankar; Yancy W. Riddle; Makhlouf M Makhlouf

2004-01-01

154

Nucleation of the paramagnetic phase in Fe–B systems during B + and N + implantation  

Microsoft Academic Search

Magnetic-to-paramagnetic phase transformation in Fe–B and Fe–B-N systems, prepared by means of successive boron and nitrogen implantations into iron films, has been studied using the methods of conversion electron Mössbauer spectroscopy (CEMS), and Auger electron spectroscopy (AES). Boron and nitrogen implantation was carried out in a dose range of 6×1016–2×1017 ions\\/cm2 with energy of 20 keV, and a mean current

V. V. Uglov; J. A. Fedotova; J. Stanek

2000-01-01

155

Bubble nucleation in stout beers  

Microsoft Academic Search

Bubble nucleation in weakly supersaturated solutions of carbon dioxide---such as champagne, sparkling wines, and carbonated beers---is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology

W. T. Lee; J. S. McKechnie; M. G. Devereux

2011-01-01

156

Residual-Impurity Effects in Directional Solidification: Long-Lasting Recoil of the Front and Nucleation-Growth of Gas Bubbles  

Microsoft Academic Search

Directional-solidification experiments are often perturbed by the nucleation of gas bubbles and other residual-impurity effects. We present a detailed experimental study of these phenomena in the system CBr{4}-C2Cl6 directionally solidified in thin films. As is usual in this type of experiments, we use zone-refined and outgased products, but do not fill and seal the samples under vacuum. We study the

Silvère Akamatsu; Gabriel Faivre

1996-01-01

157

An Investigation of Gas Phase Ozonolysis Reactions.  

National Technical Information Service (NTIS)

A simple gas phase stopped-flow apparatus has been used to determine the rates and stoichiometry for the reactions of ozone with ethylene, propene, 1-butene, methylpropene, cis-2-butene, and trans-2-butene. Measurements of the intensity of light scattered...

D. G. Williamson

1976-01-01

158

Nuclear liquid-gas phase transition  

SciTech Connect

Calculations of the equation of state of nuclear matter strongly suggest the existence of a liquid-gas phase transition. However, how sharp the transition will appear in finite nuclei, and what the experimental signatures will be are questions which evoke considerable debate. The current status of these issues, particularly the experimental signature ambiguities, is reviewed here.

Boal, D.H.

1984-11-15

159

EPA GAS PHASE CHEMISTRY CHAMBER STUDIES  

EPA Science Inventory

Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

160

Continuous-Flow Gas-Phase Bioreactors  

NASA Technical Reports Server (NTRS)

Continuous-flow gas-phase bioreactors proposed for biochemical, food-processing, and related industries. Reactor contains one or more selected enzymes dehydrated or otherwise immobilized on solid carrier. Selected reactant gases fed into reactor, wherein chemical reactions catalyzed by enzyme(s) yield product biochemicals. Concept based on discovery that enzymes not necessarily placed in traditional aqueous environments to function as biocatalysts.

Wise, Donald L.; Trantolo, Debra J.

1994-01-01

161

Homogeneous nucleation of nitrogen  

NASA Astrophysics Data System (ADS)

We investigated the homogeneous nucleation of nitrogen in a cryogenic expansion chamber [A. Fladerer and R. Strey, J. Chem. Phys. 124, 164710 (2006)]. Gas mixtures of nitrogen and helium as carrier gas were adiabatically expanded and cooled down from an initial temperature of 83 K until nucleation occurred. This onset was detected by constant angle light scattering at nitrogen vapor pressures of 1.3-14.2 kPa and temperatures of 42-54 K. An analytical fit function well describes the experimental onset pressures with an error of +/-15%. We estimate the size of the critical nucleus with the Gibbs-Thomson equation yielding critical sizes of about 50 molecules at the lowest and 70 molecules at the highest temperature. In addition, we estimate the nucleation rate and compare it with nucleation theories. The predictions of classical nucleation theory (CNT) are 9 to 19 orders of magnitude below the experimental results and show a stronger temperature dependence. The Reguera-Reiss theory [Phys. Rev. Lett. 93, 165701 (2004)] predicts the correct temperature dependence at low temperatures and decreases the absolute deviation to 7-13 orders of magnitude. We present an empirical correction function to CNT describing our experimental results. These correction parameters are remarkably close to the ones of argon [Iland et al., J. Chem. Phys. 127, 154506 (2007)] and even those of water [J. Wölk and R. Strey, J. Phys. Chem. B 105, 11683 (2001)].

Iland, Kristina; Wedekind, Jan; Wölk, Judith; Strey, Reinhard

2009-03-01

162

Homogeneous nucleation of nitrogen.  

PubMed

We investigated the homogeneous nucleation of nitrogen in a cryogenic expansion chamber [A. Fladerer and R. Strey, J. Chem. Phys. 124, 164710 (2006)]. Gas mixtures of nitrogen and helium as carrier gas were adiabatically expanded and cooled down from an initial temperature of 83 K until nucleation occurred. This onset was detected by constant angle light scattering at nitrogen vapor pressures of 1.3-14.2 kPa and temperatures of 42-54 K. An analytical fit function well describes the experimental onset pressures with an error of +/-15%. We estimate the size of the critical nucleus with the Gibbs-Thomson equation yielding critical sizes of about 50 molecules at the lowest and 70 molecules at the highest temperature. In addition, we estimate the nucleation rate and compare it with nucleation theories. The predictions of classical nucleation theory (CNT) are 9 to 19 orders of magnitude below the experimental results and show a stronger temperature dependence. The Reguera-Reiss theory [Phys. Rev. Lett. 93, 165701 (2004)] predicts the correct temperature dependence at low temperatures and decreases the absolute deviation to 7-13 orders of magnitude. We present an empirical correction function to CNT describing our experimental results. These correction parameters are remarkably close to the ones of argon [Iland et al., J. Chem. Phys. 127, 154506 (2007)] and even those of water [J. Wolk and R. Strey, J. Phys. Chem. B 105, 11683 (2001)]. PMID:19317546

Iland, Kristina; Wedekind, Jan; Wölk, Judith; Strey, Reinhard

2009-03-21

163

Gas phase chemistry of the transactinides  

NASA Astrophysics Data System (ADS)

In the past few years the gas phase chemistry of the first three transactinide elements rutherfordium (element 104), dubnium (element 105) and seaborgium (element 106) has been studied experimentally using OLGA, the On-line Gas chemistry Apparatus, developed at Paul Scherrer Institute. In each experiment, the investigated transactinide element was identified by measuring the characteristic decay properties of its isotopes. In the chemistry of rutherfordium and dubnium evidence for relativistic effects were found, as predicted previously in theoretical calculations. For the first time, the volatility of Sg oxychlorides in comparison to its lighter homologues W and Mo was measured. Also, the half-lives and SF-branches of the nuclides 265Sg and 266Sg were determined. Finally, prospects for a chemical separation of bohrium (element 107) and hassium (element 108) using gas phase chemistry will be discussed.

Türler, A.

1999-01-01

164

Nucleation and hysteresis of vapor-liquid phase transitions in confined spaces: Effects of fluid-wall interaction  

NASA Astrophysics Data System (ADS)

In this work, we propose a method to stabilize a nucleus in the framework of lattice density-functional theory (LDFT) by imposing a suitable constraint. Using this method, the shape of critical nucleus and height of the nucleation barrier can be determined without using a predefined nucleus as input. As an application of this method, we study the nucleation behavior of vapor-liquid transition in nanosquare pores with infinite length and relate the observed hysteresis loop on an adsorption isotherm to the nucleation mechanism. According to the dependence of hysteresis and the nucleation mechanism on the fluid-wall interaction, w , in this work, we have classified w into three regions ( w>0.9 , 0.1?w?0.9 , and w<0.1 ), which are denoted as strongly, moderately, and weakly attractive fluid-wall interaction, respectively. The dependence of hysteresis on the fluid-wall interaction is interpreted by the different nucleation mechanisms. Our constrained LDFT calculations also show that the different transition paths may induce different nucleation behaviors. The transition path dependence should be considered if morphological transition of nuclei exists during a nucleation process.

Men, Yumei; Yan, Qingzhao; Jiang, Guangfeng; Zhang, Xianren; Wang, Wenchuan

2009-05-01

165

Nucleation and growth of Ag islands on the (.sqroot.3 × .sqroot.3)R30° phase of Ag on Si(111)  

SciTech Connect

We use scanning tunneling microscopy to measure densities and characteristics of Ag islands that form on the ({radical}3 x {radical}3)R30{sup o}-Ag phase on Si(111), as a function of deposition temperature. Nucleation theory predicts that the logarithm of island density varies linearly with inverse deposition temperature. The data show two linear regimes. At 50-125 K, islands are relatively small, and island density decreases only slightly with increasing temperature. At 180-250 K, islands are larger and polycrystalline, and island density decreases strongly with increasing temperature. At 300 K, Ag atoms can travel for distances of the order of 1 {micro}m. Assuming that Ag diffusion occurs via thermally activated motion of single atoms between adjacent sites, the data can be explained as follows. At 50-125 K, the island density does not follow conventional Arrhenius scaling due to limited mobility and a consequent breakdown of the steady-state condition for the adatom density. At {approx} 115-125 K, a transition to conventional Arrhenius scaling with critical nucleus size (i = 1) begins, and at 180-250 K, i > 1 prevails. The transition points indicate a diffusion barrier of 0.20-0.23 eV and a pairwise Ag-Ag bond strength of 0.14 eV. These energy values lead to an estimate of i {approx} 3-4 in the regime 180-250 K, where island density varies strongly with temperature.

Belianinov, A.; Unal, B.; Ho, K.-M.; Wang, C.-Z.; Evans, J. W.; Tringides, M. C.; Thiel, P. A.

2011-06-06

166

Surface bubble nucleation stability.  

PubMed

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobized silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this parameter space, occurring for gas concentrations of approximately 100%-110%. Below the nanobubble region we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles. PMID:21405411

Seddon, James R T; Kooij, E Stefan; Poelsema, Bene; Zandvliet, Harold J W; Lohse, Detlef

2011-02-01

167

From gas-phase oxidation of SO2 by SO4- to the formation of sulfuric acid  

NASA Astrophysics Data System (ADS)

One of the difficulties to predict atmospheric nucleation is related to inaccurate measure of the total sulfuric acid concentration. We present a density functional theory investigation of the SO2 gas phase oxidation by SO4-. In the immediate product, SO2.SO4- cluster, SO2 is subsequently oxidized and SO3SO3- is formed at 1.7 × 10-7 s-1 reaction rate. SO3SO3- interacts with O2 molecule to form SO3 and SO5-, which are important species in the gas phase chemistry of sulfur and in the formation mechanism of sulfuric acid.

Tsona, Narcisse; Bork, Nicolai; Vehkamäki, Hanna

2013-05-01

168

An in vitro Study of a Phase-Shift Nanoemulsion: A Potential Nucleation Agent for Bubble-Enhanced HIFU Tumor Ablation  

Microsoft Academic Search

Phase-shift nanoemulsions have the potential to nucleate bubbles and enhance high-intensity focused ultrasound (HIFU) cancer therapy. This emulsion consists of albumin-coated dodecafluoropentane (DDFP) droplets with a mean diameter of approximately 260 nm at 37°C. It is known that superheated perfluorocarbon droplets can be vaporized with microsecond long ultrasound pulses if the acoustic pressure exceeds a specific threshold. In addition, it

Peng Zhang; Tyrone Porter

2010-01-01

169

Experimental Thermochemistry of Gas Phase Cytosine Tautomers  

NASA Astrophysics Data System (ADS)

Enthalpies of interconversion are measured for the three lowest energy tautomers of isolated cytosine. The equilibrium distribution of tautomers near 600 K is frozen upon the capture of the gas phase species by low temperature helium nanodroplets. The temperature dependence of the gas phase cytosine tautomer populations is determined with infrared laser spectroscopy of the helium solvated species. The interconverison enthalpies obtained from the van't Hoff relation are 1.14 ± 0.21 and 1.63 ± 0.12 for the C31 rightleftharpoons C32 and C31 rightleftharpoons C1 equilibria, respectively. C31 and C32 are rotamers of an enol tautomer, and C1 is a keto tautomer. The interconversion enthalpies are compared to recent CCSD(T) thermochemistry calculations of cytosine tautomers.

Morrison, A. M.; Douberly, G. E.

2011-06-01

170

Gas-phase dehydrocyclization of diphenylamine  

Microsoft Academic Search

The gas-phase dehydrocyclization of diphenylamine to carbazole was studied in a fix-bed reactor over Pt and Pd catalysts. Alumina, magnesium oxide and silica were used as supports. The reaction was carried out at a temperature of 560°C in the presence of hydrogen. Pd catalysts are reasonably active but not selective compared to Pt catalysts which possess very high activity and

Miroslav Vl?ko; Zuzana Cvengrošová; Milan Hronec; Piyasan Praserthdam

2007-01-01

171

Gas-phase separations of protease digests  

Microsoft Academic Search

A mixture of peptides from a complete tryptic digest of ubiquitin has been analyzed by ion mobility\\/time-of-flight mass spectrometry\\u000a techniques. All components of the mixture were electrosprayed and ions were separated in the gas phase based on differences\\u000a in their mobilities through helium before being dispersed into a time-of-flight mass spectrometer for mass-to-charge analysis.\\u000a The data show that ions separate

Stephen J. Valentine; Anne E. Counterman; Cherokee S. Hoaglund; James P. Reilly; David E. Clemmer

1998-01-01

172

From the gas phase to aqueous solution  

NASA Astrophysics Data System (ADS)

Structural investigations of isolated and hydrated glucose, galactose and lactose structures in the gas phase based upon infra-red ion dip (IRID) spectroscopy conducted at low temperatures, are linked with parallel investigations conducted in aqueous solution at 298 K based upon measurements of their vibrational Raman and Raman optical activity (ROA) spectra. [`]Basis sets' of computed (gas phase) Raman and ROA spectra associated with their low-lying conformational structures are used to construct [`]weighted sums' which can approximate their experimental Raman and ROA spectra recorded in solution and provide estimates of their conformational population distributions in aqueous solution at 298 K; they are compared with estimates based upon analysis of NMR measurements and molecular mechanics and molecular dynamics calculations. The altered conformational preferences in the singly hydrated complexes of glucose and galactose isolated in the gas phase, appear to be sustained in aqueous solution, supporting the view that explicit hydration provides a key influence on their conformational preferences in solution. On the other hand, the conformational preference of the isolated [beta](1 --> 4) disaccharide, lactose which resists conformational alteration when singly hydrated, is altered when it is transferred to aqueous solution at 298 K. The computational evidence suggests the control is exerted by entropic effects associated with a loosening of the structure around the glycosidic linkage.

MacLeod, Neil A.; Johannessen, Christian; Hecht, Lutz; Barron, Laurence D.; Simons, John P.

2006-07-01

173

Gaseous bubble nucleation under shear flow  

Microsoft Academic Search

A decompression experiment of a water solution, saturated with methane gas at about 68atm at room temperature, was done to investigate gas bubble nucleation under shear flow. A pressure reduction from 68atm to atmospheric pressure is well below the decompression pressure required for spontaneous bubble nucleation of the methane gas, about 120atm. The application of a shear flow from 5min

Ho-Young Kwak; Ki-Moon Kang

2009-01-01

174

The impact of microphysical parameters, ice nucleation mode, and habit growth on the ice/liquid partitioning in mixed-phase Arctic clouds  

NASA Astrophysics Data System (ADS)

The fundamental physical processes that maintain supercooled liquid in observed Arctic mixed-phase clouds are poorly constrained. To isolate the factors that control ice/liquid partitioning during the ascent of an air parcel, we apply an adiabatic parcel model that includes ice nucleation by deposition and immersion freezing and ice habit evolution. Simulations are performed for two different temperature regimes that resemble those observed during the Mixed-Phase Arctic Cloud Experiment (-13°C < T < -9°C) and the Surface Heat Budget of the Arctic Ocean (-22°C < T < -17°C). Effects on ice and liquid water evolution in an updraft are explored as a function of ice nucleus (IN) concentration and nucleation mode, updraft velocity, properties of cloud condensation nuclei, and assumption about ice particle shape (habit). For most conditions, ice and liquid coexist and increase simultaneously, and only at high IN concentrations or low updraft velocities do ice particles grow at the expense of droplets. The impact of the ice nucleation mode on ice/liquid distribution depends on the temperature and supersaturation regime. The assumption of spherical ice particles instead of nonspherical habits leads to an underestimate of ice growth. It is concluded that updraft velocity, IN concentrations, and particle shape can impact ice/liquid distribution to similar extents.

Ervens, Barbara; Feingold, Graham; Sulia, Kara; Harrington, Jerry

2011-09-01

175

The effect of lattice and grain boundary diffusion on the redistribution of Xe in metallic nuclear fuels: Implications for the use of ion implantation to study fission-gas-bubble nucleation mechanisms  

Microsoft Academic Search

A multi-atom gas bubble-nucleation mechanism has been proposed as part of a predictive fission-gas release model for metallic nuclear fuels. Validation of this mechanism requires experimental measurement of fission-gas bubble-size distributions at well-controlled gas concentrations and temperatures. There are advantages to carrying out such a study using ion implantation as the source of gas atoms compared with neutron irradiations. In

Wayne E. King; Scott J. Tumey; Jeffrey Rest; George H. Gilmer

2011-01-01

176

Nucleation in Microcellular Thermoplastic Foams  

NASA Astrophysics Data System (ADS)

Amorphous, thermoplastic polymers are foamed using inert gases such as carbon dioxide or nitrogen to create a microcellular foam. The small cell size, smaller than critical flaws already present in most polymers, allows the microcellular foam to retain some critical mechanical properties present in the bulk material. Microcellular foams with a cell density greater than 10^8 cells/cm^3 and an average cell size of order 10 microns or less, have been succesfully produced in amorphous polymers such as polystyrene, poly(methyl methacrylate) and polycarbonate. Current processing methods make it difficult to achieve a high cell nucleation density. In an effort to control the cell nucleation density, heterogeneous nucleation sites, both solid particle sites and in the form of block copolymer micelles, have been added to polystyrene samples. Batch experiments using carbon dioxide gas reveal anomalous trends in nucleation behavior that can not be explained by the classical nucleation theory, prompting further inquiry into its validity.

Spitael, Pieter; Macosko, Christopher W.

2000-03-01

177

Quantum nucleation and dissipation in the phase separation of supersaturated liquid 3He? 4He solution at low temperatures  

NASA Astrophysics Data System (ADS)

The quantum stratification of supersaturated metastable liquid sol is considered. The effects of the energy dissipation on the nucleat rate are incorporated. For weak supersaturations diffusion determi decay probability in normal solution. In superfluid solution heat conduction must be also involved.

Burmistrov, Serguei N.; Dubovskii, Leonid B.

1990-08-01

178

Gas phase thermochemistry of organogermanium compounds  

SciTech Connect

A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

Engel, J.P.

1993-12-07

179

Gas-phase photolysis of tungsten hexachloride  

NASA Astrophysics Data System (ADS)

The laser-induced decomposition of WCl6 in the gas-phase is investigated by means of absorption, Raman and laser-induced fluorescence spectroscopy. With visible Ar+-laser radiation dissociation of WCl6 into WCl4 and Cl2 has been observed. Further decomposition can be achieved in the presence of H2 employing ultraviolet Ar+-laser radiation at 360 nm. A complete reduction to W requires even shorter wavelengths. The experimental results are analyzed on the basis of model calculations. Implications on the Laser-induced Chemical Vapor Deposition (LCVD) of W are discussed.

Kullmer, R.

1994-07-01

180

Solid-phase sequencing on the gas-phase sequencer.  

PubMed

Automated Edman degradation has been successfully used for determining the primary structure of numerous peptides and proteins. Quantitative solid-phase Edman degradation has great potential use for amino acid sequence analysis of synthetic peptides assembled on resin support by the Merrifield procedure. We report here the combined use of a modified gas-phase sequencer program and our improved reversed-phase HPLC analysis for PTH-amino acids to carry out the sequence analysis on synthesized peptide resins. This approach is far more sensitive than using glass beads on the conventional solid-phase sequencer. The peptide was assembled on copoly (styrene-1% divinylbenzene) resin beads at an initial substitution of 0.54 mmol/g. On a routine basis, 10-15 resin beads are used, and a repetitive yield of 94% is obtained: as few as 4 beads can be successfully sequenced. The HPLC PTH-amino acid analysis is sensitive down to subpicomole quantities. This procedure offers a sensitive and rapid analytical tool for checking the purity of peptides as they are being assembled on solid support. PMID:2942055

Sarin, V K; Kim, Y; Fox, J L

1986-05-01

181

Vaccum Gas Tungsten Arc Welding, phase 1  

NASA Technical Reports Server (NTRS)

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-01-01

182

Buckyball Nucleation of HiPco Tubes  

NASA Technical Reports Server (NTRS)

The purpose of this innovation is to enhance nucleation of single-wall nanotubes (SWNTs) in the HiPco process, selectively producing 10,10 tubes, something which until now has not been thought possible. This is accomplished by injecting C60, or a derivative of C60, solubilized in supercritical CO2 together with a transition metal carboneal cocatalyst into the HiPco reactor. This is a variant on the supercritical disclosure. C60 has never been used to nucleate carbon nanotubes in the gas phase. C60 itself may not have adequate solubility in supercritical CO2. However, fluorinated C60, e.g., C60F36, is easy to make cheaply and should have much enhanced solubility.

Smalley, Richard E.

2012-01-01

183

Homogeneous bubble nucleation in rhyolitic melt: Experiments and nonclassical theory  

NASA Astrophysics Data System (ADS)

The transfer of volatiles from the Earth's interior to the atmosphere occurs through degassing of magma, the dynamics of which assert a significant control on volcanic eruptions. The first and most critical step in degassing is the nucleation of gas bubbles, which requires that a sufficient number of volatile molecules cluster together to overcome the free energy associated with the formation of a new interface between nucleus and surrounding melt. This free energy is a function of surface tension, typically assumed to equate to the macroscopically measurable value. Surface tension estimates inferred from bubble nucleation experiments in silicate melts are, however, lower than direct macroscopic measurements, making it difficult to accurately predict magma ascent and decompression rates from measured bubble number densities in pyroclasts. We provide a potential resolution to this problem through an integrated study of bubble nucleation experiments and modeling thereof, based on nonclassical nucleation theory. We find that surface tension between critical bubble nuclei and the surrounding melt depends on the degree of supersaturation and is lower than the macroscopically measured value. This is consistent with the view that far from equilibrium the interface between a nucleus and surrounding metastable bulk phase is diffuse instead of sharp. As a consequence, the increase in nucleation rate with supersaturation is significantly larger at high supersaturations than predicted by classical nucleation theory.

Gonnermann, H. M.; Gardner, J. E.

2013-11-01

184

Nucleation in the presence of long-range interactions. [performed on ferroelectric barium titanate  

NASA Technical Reports Server (NTRS)

Unlike droplet nucleation near a liquid-gas critical point, the decay of metastable phases in crystalline materials is strongly affected by the presence of long-range forces. Field quench experiments performed on the ferroelectric barium titanate indicate that nucleation in this material is markedly different from that observed in liquids. In this paper, a theory for nucleation at a first-order phase transition in which the mediating forces are long range is presented. It is found that the long-range force induces cooperative nucleation and growth processes, and that this feedback mechanism produces a well-defined delay time with a sharp onset in the transformation to the stable phase. Closed-form expressions for the characteristic onset time and width of the transition are developed, in good agreement with numerical and experimental results.

Chandra, P.

1989-01-01

185

Assembling gas-phase reaction mechanisms for high temperature inorganic systems based on quantum chemistry calculations and reaction rate theories  

NASA Astrophysics Data System (ADS)

Detailed chemical kinetic modeling based on computational quantum chemistry has been quite successful in making quantitative predictions about some systems, particularly the combustion of small hydrocarbons and certain areas of atmospheric chemistry. The gas phase chemistry of many processes in high-temperature inorganic systems, from materials synthesis to propulsion to waste incineration, could in principle be modeled with equal or greater success using detailed chemical kinetic modeling. This contribution provides examples from our own work of how computational quantum chemistry can be used in developing gas phase reaction mechanisms for modeling of high temperature materials processing. In the context of CVD of silicon from dichlorosilane, CVD of alumina from AlCl3/H2/CO2 mixtures, and particle nucleation from silane, this detailed chemical kinetic modeling has given us insight into gas phase reaction pathways that we would not likely have gained by other means.

Swihart, Mark T.

2005-02-01

186

A Review Study of Nucleation and Its Role in Solidification.  

National Technical Information Service (NTIS)

A review study of nucleation and its role in determining grain size in solidification is presented. It is demonstrated that nucleation is an essential aspect of most phase transformation processes when the unstable phase is initially free of all fragments...

K. A. Van Wormer

1969-01-01

187

Regional air quality - Atmospheric nucleation interactions  

NASA Astrophysics Data System (ADS)

Nanoparticles have been studied for the importance of the health effects and global energy balances. New particle formation from gas species, also known as nucleation, is one of the important pathways to the budget of the nanoparticles as well as direct emissions. This work focuses on the details of nucleation events such as nucleation rate and involving gas species using computational programs. A computationally efficient new multi-component aerosol dynamics model that simulates the full aerosol size distribution and composition starting at a diameter of 0.8 nm, Dynamic Model for Aerosol Nucleation (DMAN), is developed. The model uses a two-moment sectional algorithm manipulating both the aerosol number and mass distributions, and successfully reproduced analytical solutions. Three chemical components, sulfate, ammonium, and non-volatile organics are tracked explicitly. Using ternary (sulfuric acid-ammonia-water) nucleation parameterization, the model is able to reproduce nucleation events from their start to completion. The simulations suggest that ammonia availability controls the nucleation bursts in the northeastern US. Six nucleation parameterization are tested using the DMAN model. Weak, moderate, and strong nucleation events together with days without nucleation from the Pittsburgh Air Quality Study (PAQS) are selected for the evaluation. The ability of the different theories to reproduce the occurrence or lack of a nucleation event is evaluated. The ternary sulfuric acid-ammonia-water theory was the only one that was successful for all days. Sensitivity tests of the remaining parameterizations suggest that increasing or decreasing the corresponding nucleation rates does not change the overall performance of the parameterizations when both the nucleation and non-nucleation days are included in the tests. A three-dimensional chemical transport model (PMCAMx-UF) is developed incorporating the DMAN model in order to investigate a special scale and frequency of nucleation events. The model can use a variety of nucleation theories and parameterizations. The model simulates seventeen days from July 12 to July 28, 2001 in the Eastern U.S using the ternary sulfuric acid-ammonia-water nucleation theory with a scaling factor. The model predicts nucleation events that extend over scales of 100s to 1000 km in the midwest and northeastern U.S. The first comparison with the PAQS measurement dataset is promising both for the frequency, time of onset and strength of the nucleation events. PMCAMx-UF correctly predicts the occurrence or lack of nucleation in Pittsburgh more than 80%, although the model has a tendency of overpredicting nucleation.

Jung, Jae-Gun

188

Four-phase fully-coupled mold-filling and solidification simulation for gas porosity prediction in aluminum sand casting  

NASA Astrophysics Data System (ADS)

The impact of mold-filling and oxide film enclosure on gas porosity in A356 was investigated using a three-phase, fully-coupled, mold-filling and solidification simulation. For the prediction of gas porosity, a fourth hydrogen phase was added. At the solidification front hydrogen is rejected from the solid and accumulates in the melt. Pores nucleate if the solute gas exceeds the solubility limit. Air and melt are separated by a volume of fluid interface and special treatment of the hydrogen phase convection was necessary to limit the hydrogen to the melt. Folding of the melt surface was used as a source for oxide film entrainment. These oxide films were transported with the melt and used as nucleation sites for gas porosity formation. The influence of melt flow due to filling and oxide film distribution was analyzed using a simple 3-block test geometry. The test geometry was cast in A356 and analyzed by computer tomography to validate the porosity prediction.

Jakumeit, J.; Jana, S.; Waclawczyk, T.; Mehdizadeh, A.; Sadiki, A.; Jouani, J.

2012-07-01

189

Diamond nucleation from the gas phase onto cold-worked Co-cemented tungsten carbide  

Microsoft Academic Search

Co-cemented tungsten carbide (WC–Co) substrates with fine (1 ?m) and coarse (6 ?m) grain size were sintered using 6 wt.% Co as a binder. The as-sintered samples were ground to the final geometry (10×10×3 mm3). After the grinding treatment, the full width at half maximum (FWHM) of the WC X-ray diffraction (XRD) peaks indicated a high level of strain in

Riccardo Polini; Pierangelo D'Antonio; Enrico Traversa

2003-01-01

190

Gas phase hyper-Rayleigh scattering measurements  

NASA Astrophysics Data System (ADS)

Measurements of hyper-Rayleigh scattering intensities and polarization ratios are presented for nine small molecules in the gas phase [CH4, CF4, CCl4, N2O, NH3, D2O, SO2, CF2Cl2, and (CH3)2CO]. In four cases [CH4, CF4, CCl4, and N2O] all molecular hyperpolarizability tensor components can be determined from the measurements. The results of this experiment are compared with the results of previous ab initio calculations, finding discrepancies up to 60%. Including vibrational contributions decreases the discrepancies for CH4 and CF4 and increases them for CCl4, D2O, and NH3.

Shelton, David P.

2012-07-01

191

Phase transitions in a gas of anyons  

SciTech Connect

We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however, now in the presence of a topological term added to the action which corresponds to the total linking number between the loops. We compute the linking number using a novel approach employing certain notions from knot theory. Adding the topological term converts the particles into anyons. Interpreting the model as an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong-coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. The system continues to exhibit a phase transition as a function of the vortex mass as it becomes small. We find the following new results. The Chern-Simons term has no effect on the Wilson loop. On the other hand, it does effect the 't Hooft loop of a given configuration, adding the linking number of the 't Hooft loop with all of the dynamical vortex loops. We find the unexpected result that both the Wilson loop and the 't Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, in both phases of the theory. It should be noted that our method suffers from numerical instabilities if the coefficient of the Chern-Simons term is too large; thus, we have restricted our results to small values of this parameter. Furthermore, interpreting the lattice loop gas as an effective theory describing the Abelian Higgs model is only known to be true in the infinite coupling limit; for strong but finite coupling this correspondence is only a conjecture, the validity of which is beyond the scope of this article.

MacKenzie, R.; Nebia-Rahal, F.; Paranjape, M. B. [Groupe de physique des particules, Departement de physique, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, H3C 3J7 (Canada); Richer, J. [Reseau quebecois de calcul de haute performance, DGTIC, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, H3C 3J7 (Canada)

2010-10-01

192

Gas development plan - Lithuania. Phase 1.  

National Technical Information Service (NTIS)

A detailed description of the plan for the development of gas utilization in Lithuania is presented. The plan is subdivided under the headings of gas supply, gas demand, gas transmission and distribution, economy and the organization of the gas sector in ...

1993-01-01

193

The VRT gas turbine combustor - Phase II  

NASA Technical Reports Server (NTRS)

An innovative annular combustor configuration is being developed for aircraft and other gas turbine engines. This design has the potential of permitting higher turbine inlet temperatures by reducing the pattern factor and providing a major reduction in NO(x) emission. The design concept is based on a Variable Residence Time (VRT) technique which allows large fuel particles adequate time to completely burn in the circumferentially mixed primary zone. High durability of the combustor is achieved by dual-function use of the incoming air. In Phase I, the feasibility of the concept was demonstrated by water analogue tests and 3D computer modeling. The flow pattern within the combustor was as predicted. The VRT combustor uses only half the number of fuel nozzles of the conventional configuration. In Phase II, hardware was designed, procured, and tested under conditions simulating typical supersonic civil aircraft cruise conditions to the limits of the rig. The test results confirmed many of the superior performance predictions of the VRT concept. The Hastelloy X liner showed no signs of distress after nearly six hours of tests using JP5 fuel.

Melconian, Jerry O.; Mongia, Hukam C.; Nguyen, Hung L.

1992-01-01

194

Gas: A Neglected Phase in Remediation of Metals and Radionuclides  

SciTech Connect

The gas phase is generally ignored in remediation of metals and radionuclides because it is assumed that there is no efficient way to exploit it. In the literal sense, all remediations involve the gas phase because this phase is linked to the liquid and solid phases by vapor pressure and thermodynamic relationships. Remediation methods that specifically use the gas phase as a central feature have primarily targeted volatile organic contaminants, not metals and radionuclides. Unlike many organic contaminants, the vapor pressure and Henry's Law constants of metals and radionuclides are not generally conducive to direct air stripping of dissolved contaminants. Nevertheless, the gas phase can play an important role in remediation of inorganic contaminants and provide opportunities for efficient, cost effective remediation. The objective here is to explore ways in which manipulation of the gas phase can be used to facilitate remediation of metals and radionuclides.

Denham, Miles E.; Looney, Brian B

2005-09-28

195

The gas-phase ozonolysis of ?-humulene.  

PubMed

?-Humulene contains three double bonds (DB), and after ozonolysis of the first DB the first-generation products are still reactive towards O(3) and produce second- and third-generation products. The primary aim of this study consisted of identifying the products of the three generations, focusing on the carboxylic acids, which are known to have a high aerosol formation potential. The experiments were performed in a 570 litre spherical glass reactor at 295 K and 730 Torr. Initial mixing ratios were 260-2090 ppb for O(3) and 250-600 ppb for ?-humulene in synthetic air. Reactants and gas-phase products were measured by in situ FTIR spectroscopy. Particulate products were sampled on Teflon filters, extracted with methanol and analyzed by LC-MS/MS-TOF. Using cyclohexane (10-100 ppm) as an OH-radical scavenger and by monitoring the yield of cyclohexanone by PTR-MS, an OH-yield of (10.5 ± 0.7)% was determined for the ozonolysis of the first DB, and (12.9 ± 0.7)% of the first-generation products. The rate constant of the reaction of O(3) with ?-humulene is known as k(0) = 1.17 × 10(-14) cm(3) molecule(-1) s(-1) [Y. Shu and R. Atkinson, Int. J. Chem. Kinet., 1994, 26, 1193-1205]. The reaction rate constants of O(3) with the first-generation products and the second-generation products were, respectively, determined as k(1) = (3.6 ± 0.9) × 10(-16) and k(2) = (3.0 ± 0.7) × 10(-17) cm(3) molecule(-1) s(-1) by Facsimile-simulation of the observed ozone decay by FTIR. A total of 37 compounds in the aerosol phase and 5 products in the gas phase were tentatively identified: 25 compounds of the first-generation products contained C13-C15 species, 9 compounds of the second-generation products contained C8-C11 species, whereas 8 compounds of the third-generation products contained C4-C6 species. The products of all three generations consisted of a variety of dicarboxylic-, hydroxy-oxocarboxylic- and oxo-carboxylic acids. The formation mechanisms of some of the products are discussed. The residual FTIR spectra indicate the formation of secondary ozonides (SOZ) in the gas phase, which are formed by the intramolecular reaction of the Criegee moiety with the carbonyl endgroup. These SOZ revealed to be stable over several hours and its formation was shown not to be affected by the addition of Criegee-radical scavengers such as HCOOH or H(2)O. This suggests that in the ozonolysis of ?-humulene at atmospheric pressures the POZ will decompose rapidly, and that a large fraction of the formed exited Criegee Intermediate will be stabilized to form stable SOZ, while the formation of OH-radicals via the hydroperoxide channel will be a minor process. PMID:21461420

Beck, M; Winterhalter, R; Herrmann, F; Moortgat, G K

2011-06-21

196

Microsecond simulations of spontaneous methane hydrate nucleation and growth.  

PubMed

Despite the industrial implications and worldwide abundance of gas hydrates, the formation mechanism of these compounds remains poorly understood. We report direct molecular dynamics simulations of the spontaneous nucleation and growth of methane hydrate. The multiple-microsecond trajectories offer detailed insight into the process of hydrate nucleation. Cooperative organization is observed to lead to methane adsorption onto planar faces of water and the fluctuating formation and dissociation of early hydrate cages. The early cages are mostly face-sharing partial small cages, favoring structure II; however, larger cages subsequently appear as a result of steric constraints and thermodynamic preference for the structure I phase. The resulting structure after nucleation and growth is a combination of the two dominant types of hydrate crystals (structure I and structure II), which are linked by uncommon 5(12)6(3) cages that facilitate structure coexistence without an energetically unfavorable interface. PMID:19815725

Walsh, Matthew R; Koh, Carolyn A; Sloan, E Dendy; Sum, Amadeu K; Wu, David T

2009-11-20

197

Bubble nucleation in stout beers.  

PubMed

Bubble nucleation in weakly supersaturated solutions of carbon dioxide-such as champagne, sparkling wines, and carbonated beers-is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets. PMID:21728549

Lee, W T; McKechnie, J S; Devereux, M G

2011-05-01

198

In situ spectroscopic ellipsometry study of GaN nucleation layer growth and annealing on sapphire in metal-organic vapor-phase epitaxy  

NASA Astrophysics Data System (ADS)

Deposition and annealing of GaN nucleation layers (NLs) on sapphire during metal-organic vapor-phase epitaxy were studied using in situ spectroscopic ellipsometry. Growth was found to start with a remarkable delay after precursor switching through the formation of an initial roughness and a subsequent coalescence, which leads to the formation of a dense nucleation layer. The initial growth rate strongly depends on growth environment pretreatment and decreases if the susceptor is coated with GaN from preceding growth runs. The evaluation of the optical properties of as-grown NLs shows that the growth rate strongly affects the crystalline quality of the NL. At decreased growth rate the band gap E0 appears more pronounced with values indicating a predominantly cubic structure. During annealing above 800 °C a structural change is observed: the thickness of the dense part of the NL increases on expense of the rough part, maintaining an almost constant total layer thickness. Simultaneously the formation of the hexagonal phase in the NL occurs. The process is accomplished at about 950 °C and is followed by a desorption of the NL at a rate of 1.4 nm/s in ammonia and nitrogen ambient at 1060 °C. The observations are confirmed by ex situ atomic force microscopy and scanning electron microscopy measurements.

Schmidtling, T.; Pohl, U. W.; Richter, W.; Peters, S.

2005-08-01

199

Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation  

Microsoft Academic Search

The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets

Y. Matsumoto

1988-01-01

200

Heterogeneous nucleation of ice from supercooled water  

NASA Astrophysics Data System (ADS)

The relaxation of a metastable phase via the formation of a critical domain of the corresponding stable phase is a phenomenon that has been studied extensively in condensed matter physics. This dissertation describes laboratory studies of this phenomenon in the context of ice nucleation from undercooled liquid water. Such a study presents unique experimental challenges because the formation of a critical embryo is a statistical event, and once it occurs the entire sample relaxes to the stable phase. In order to study this statistical process it is necessary to create a large ensemble of separate, yet identical, domains of the metastable phase. The design of an apparatus is described which creates such an ensemble, in time, by repeatedly freezing and thawing a single water drop. This apparatus allows for the collection of a large data set and therefore can identify subtle changes in nucleation statistics that are produced by external controls. This dissertation describes a series of experiments intended to probe several aspects of ice nucleation. Results are presented for homogeneous ice nucleation as well as heterogeneous ice nucleation by; silanized and unsilanized glass, aliphatic alcohol Langmuir films, ionizing radiation, electric fields and motion at the three phase contact line. These experiments are analyzed largely in the context of classical nucleation theory. The unique experimental technique described here allows for sensitive tests of the temperature dependent nucleation rates, R( T), in these systems. Analysis of the R( T) within the context of classical nucleation theory constrains thermodynamic parameters and provides insight into these nucleation processes.

Seeley, Lane Howard

201

Gas phase atomic and molecular processes  

NASA Astrophysics Data System (ADS)

We perform fully quantum mechanical calculations of the lithium 2 p -2 s and sodium 3 p -3 s resonance lines pressure broadened by collisions with helium atoms. Using carefully constructed potential energy surfaces and transition dipole moments, we have obtained the emission and absorption coefficients at temperatures from 200 to 3000 K at wavelengths between 500 and 1000 nm for lithium and at temperatures from 158 to 3000 K at wavelengths between 500 and 760 nm for sodium. Contributions from quasi-bound levels are included. Our results are in good agreement with experiment. These broadened line profiles are important in developing effective diagnostics on the temperatures, densities, albedos and composition of the atmospheres of brown dwarfs and extrasolar giant planets. We compute the diffusion coefficients of ground and excited-state lithium and sodium atoms in a helium gas. They are valuable in predicting the sign and magnitude of the light-induced drift for the gas mixture. We calculate the dispersion coefficients of the long range interactions of alkali-metal atoms with molecular hydrogen and helium atoms. The uncertainties in our results are less than 2%. We study the relaxation of the v = 1 vibrational level of carbon monoxide induced by collisions with helium three atoms in ultracold temperatures. We confirm the Wigner's threshold law which states that in the zero temperature limit the inelastic quenching cross sections are inversely proportional to the velocity of the incident atom. Our calculations agree well with experiment and we find enhanced rate coefficients as compared to those for 4 He-CO. We study the chemistry of hydrogen fluoride in the interstellar medium. We consider fine-structure collisions and find that most fluorine atoms reside in the ground 2 P 3/ 2 state. We calculate the rate coefficients for the reaction of F( 2 P 3/2 ) atoms in collisions with H 2 . Our results agree well with experiment. We confirm the conclusions of Neufeld et al. that in interstellar clouds HF is the major form of gas phase fluorine.

Zhu, Cheng

202

Recent progress in understanding particle nucleation and growth  

PubMed Central

In the past half decade, several new tools have become available for investigating particle nucleation and growth. A number of joint field and laboratory studies exploiting some of these new measurement capabilities will be described and new insights shared. the ability to measure OH, SO2, H2SO4 and aerosol number and size distributions has made possible a comparison between H2SO4 production and loss onto particles in continental air masses. In regions remote from urban emissions, agreement is typically quite good. In contrast, joint field measurements of nucleation precursors such as gas phase H2SO4 and ultrafine particles suggest that classical bimolecular nucleation theory may not properly describe the tropospheric nucleation process. An alternative mechanism, possibly involving ammonia as a stabilizing agent for H2SO4/H2O molecular clusters is discussed. Finally, ultrafine particle measurements are shown to offer new opportunities for studying particle growth rates. Preliminary results suggest that in a remote continental air mass, gas phase H2SO4 uptake is far too slow to explain observed growth rates.

Eisele, F. L.; McMurry, P. H.

1997-01-01

203

Pressure Drop, Heat Transfer, Critical Heat Flux, and Flow Stability of Two-Phase Flow Boiling Of Water and Ethylene Glycol/Water Mixtures - Final Report for Project 'Efficient Cooling In Engines with Nucleate Boiling.'  

National Technical Information Service (NTIS)

Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and t...

D. M. France J. L. Routbort W. Yu

2011-01-01

204

Theoretical Studies of Gas Phase Bioanions  

NASA Astrophysics Data System (ADS)

Theoretical studies provide insight into anionic states formed by some peptides and nucleic acid bases. A coexistence of conventional valence states and dipole-bound states will be demonstrated for some nucleic acid bases. It will be shown that the instability of zwitterion forms of amino acids in the gas phase relative to their canonical tautomers could be suppressed by attaching an excess electron. As demonstrated for zwitterions of glycine, betaine, and arginine, the solvation by an excess electron provides an extra stabilization by 6-8 kcal/mol relative to the corresponding canonical structures. Simple chemical reactions induced by electron attachment will be discussed. First, we will show that the tautomerization between zwitterionic and canonical forms of isolated amino acids is facilitated by excess electron attachment. For arginine, for example, the anionic tautomers are quasidegenerate in their electronic energies, and the reaction barrier is significantly lowered in comparison with the neutral species. Second, an intermolecular proton transfer induced by electron attachment in the uracil-glycine complex will be discussed. The theoretical results will be compared with the state-of-the-art experimental data from photoelectron spectroscopy and Rydberg electron transfer experiments.

Gutowski, Maciej

2002-03-01

205

Gas chromatography with programming the mobile phase flow rate  

Microsoft Academic Search

The dependence of stationary phase bleeding on the carrier gas flow rate and column temperature is investigated. When the carrier gas flow rate is programmed the requirements on the thermostability of the stationary phase are less stringent than in case of temperature programming. Equations for the calculation of the main parameters for a linear program are derived. An exemple for

S. A. Volkov; Yu. A. Sultanovich; K. I. Sakodinskii

1979-01-01

206

Pressure Dependence of Gas-Phase Reaction Rates  

ERIC Educational Resources Information Center

It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

2004-01-01

207

Liquid phase methanation of high concentration CO synthesis gas  

Microsoft Academic Search

Chem Systems Inc. believes that the Liquid Phase Methanation process can become an economic, reliable, and versatile method of converting synthesis gas mixtures to high-Btu gas. The process consists essentially of pumping an inert liquid upward through a reactor at a velocity sufficient to fluidize the catalyst and remove the reaction heat. A low-Btu gas is passed concurrently up the

D. B. Blum; M. B. Sherwin; M. E. Frank

1974-01-01

208

A comparison of the ice nucleating efficiencies of dust, polluted dust and smoke in mixed-phase clouds based on spaceborne lidar observations  

NASA Astrophysics Data System (ADS)

The thermodynamic phase composition of mixed-phase clouds largely determines their radiative properties and therefore their impact on the Earth's climate. Mineral dust aerosols in the Earth's atmosphere have been suggested by previous laboratory studies, field campaigns and modelling simulations to be efficient ice nuclei of natural origin that influence the fraction of ice in mixed-phase clouds. Time correlations of global vertically-resolved cloud thermodynamic phase with individually analyzed dust, polluted dust and smoke frequencies over approximately 5 years (December 1 2007 to December 31, 2012) in the mixed-phase cloud temperature regime were performed on retrievals from NASA's CALIPSO. Our results suggest that it can be seen from space that dust aerosols in the Earth's atmosphere are efficient ice nuclei and furthermore, that dust aerosols in polluted regions tend to be less efficient at ice nucleation, which is also supported by previous studies. In addition, we find that smoke aerosols, like dust aerosols, are also acting as ice nuclei in the Earth's atmosphere, although less efficiently than dust.

Tan, I.; Storelvmo, T.; Choi, Y.

2013-12-01

209

Experimental investigation and modeling of diamond nucleation on silica substrates  

NASA Astrophysics Data System (ADS)

Thin films created using chemical vapor deposition (CVD) have numerous applications. In order for these films to function effectively it is often necessary to better control their properties. This can be accomplished through a more thorough understanding of the initial stages of a film's growth. At this stage, when nucleation occurs, the microstructure of a film is determined and this has a significant influence on its properties. Two materials which are currently grown using CVD are diamond and silicon nitride. In this research, an investigation of the nucleation of both of these materials is conducted. Deposition of diamond was carried out with a microwave plasma system, while silicon nitride was nucleated using an impinging-jet reactor. Several characterization techniques were employed, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), parallel electron energy loss spectroscopy (PEELS) and optical emission spectroscopy (OES). The primary focus of the work was on diamond nucleation. Deposition was conducted on three different substrates, including silicon, oxidized silicon and silica. Several differences in experimental results were observed between the substrates. In order to explain these variations a kinetic model was developed which considers the influence of the substrate on the local gas phase chemistry. The model reveals that the concentration of oxygen is greater near silica substrates. TEM and PEELS show the presence of amorphous carbon islands on silica substrates after a pretreatment step. It is probable that these serve as nucleation sites for crystalline diamond. An additional kinetic model was developed which considers the islands as mixtures of spsp2 and spsp3 carbon. It was found that the lower surface energy of graphite and higher supersaturation ratio of diamond lead to an enhancement of nucleation. Silicon nitride was deposited on an interlayer that was found to consist of amorphous silicon nitride and crystalline silicon. The structure of the interlayer changed as it was deposited until eventually nucleation of crystalline Sisb3Nsb4 became favorable.

Koritala, Rachel Elizabeth

1997-08-01

210

Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold.  

PubMed

Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd(+) in the gas phase. While a lysozyme-Au adduct forms Au18(+), Au25(+), Au38(+) and Au102(+) ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag(+), Pt(2+), Pd(2+), Cu(2+), Fe(2+), Ni(2+) and Cr(3+)) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38(+). While other metal ions like Cu(2+) help forming Au25(+) selectively, Fe(2+) catalyzes the formation of Au25(+) over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution. PMID:24146135

Baksi, Ananya; Pradeep, T

2013-12-21

211

[On road particle emission characteristics of a Chinese phase IV natural gas bus].  

PubMed

An on-road experimental research was made on a Chinese phase IV natural gas bus using a Portable Emission Measurement System (PEMS), and particle emission characteristics under different vehicle speed, acceleration and vehicle specific power were investigated. The results show that particle number and mass emission rates increase and their emission factors decrease while the speed of the bus rises. Particle number concentration of different sizes shows multimodal logarithmic distribution pattern when the bus runs on all operation conditions (idle, low speed, medium speed and high speed), and nucleation mode particle account for a large proportion in the total particle number. With the increase of acceleration, particle emission rate rises, and it is lower when the bus runs at constant speed or slow deceleration condition than that at the fast acceleration condition. Furthermore, particle emission rate increases against the absolute value of the vehicle specific power (VSP). PMID:24881371

Lou, Di-Ming; Cheng, Wei; Feng, Qian

2014-03-01

212

Nucleation stage in supersaturated vapor with inhomogeneities due to nonstationary diffusion onto growing droplets  

NASA Astrophysics Data System (ADS)

An analytical description of the nucleation stage in a supersaturated vapor with instantly created supersaturation is given with taking into account the vapor concentration inhomogeneities arising as a result of depletion due to nonstationary diffusion onto growing droplets. This description is based on the fact, that the intensity of the nucleation of new droplets is suppressed in spherical diffusion regions of a certain size surrounding previously nucleated droplets, and remains at the initial level in the remaining volume of the vapor–gas medium. The value of the excluded volume (excluded from nucleation) depends on the explicit form of the vapor concentration profile in the space around the growing droplet, and we use for that the unsteady self-similar solution of the time-dependent diffusion equation with a convective term describing the flow of the gas–vapor mixture caused by the moving surface of the single growing droplet. The main characteristics of the phase transition at the end of the nucleation stage are found and compared with those in the theory of nucleation with homogeneous vapor consumption (the theory of mean-field vapor supersaturation). It is shown that applicability of the mean-field approach depends on smallness of the square root of the ratio of the densities of metastable and stable phases. With increasing the temperature of the supersaturated vapor or for liquid or solid solutions, this smallness weakens, and then it would be more correct to use the excluded volume approach.

Kuchma, Anatoly; Markov, Maxim; Shchekin, Alexander

2014-05-01

213

Real-Time Characterization of Particle and Gas Phase Diesel Emissions - Understanding the Influence of a Diesel Particulate Filter  

NASA Astrophysics Data System (ADS)

Diesel engine emissions constitute an important source of particulate black carbon (BC) and gas phase organics in the atmosphere. Particles composed of black carbon absorb incoming solar radiation having a net positive radiative forcing effect on the climate. Black carbon also has major air quality implications as BC particles from combustion sources are often coated with poly-aromatic hydrocarbons (PAHs), and are generally emitted in higher concentrations close to population centers. Regulations of diesel emissions target the mass of particulate matter (PM) and concentration of volatile gas phase organic compounds (VOC) produced. A third, potentially important component of diesel exhaust, is low volatility organic compounds (LVOC). Both the VOCs and LVOCs can lead to the formation of ultrafine particles (via homogeneous nucleation) and secondary organic aerosols (via oxidation). Recent development of mass spectrometric techniques to measure particulate black carbon and gas phase organics provide the opportunity to quantify and chemically characterize diesel emissions in real-time. Measurements of both the particulate and gas phase emissions from a medium-duty diesel engine will be presented. The experimental apparatus includes a diesel particulate filter (DPF) integrated in the exhaust line, which is a requirement for all 2007 and newer on-road diesel engines in the U.S. Measurements taken over the regeneration cycle of the DPF provide insight into how this after-treatment technology influences the gas phase and particle phase composition of the emissions. Gas phase measurements were made with a newly developed Total Gas-Phase Organic (TGO) instrument. Particulate species were characterized with a Soot Particle Aerosol Mass Spectrometer (SP-AMS). The combined utility of the TGO and SP-AMS instruments for emissions characterization studies will be demonstrated.

Cross, E. S.; Sappok, A.; Carrasquillo, A. J.; Onasch, T. B.; Fortner, E.; Jayne, J.; Wong, V.; Worsnop, D. R.; Kroll, J. H.

2010-12-01

214

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys.  

National Technical Information Service (NTIS)

From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase,...

K. F. Kelton A. K. Gangopadhyay G. W. Lee R. W. Hyers T. J. Rathz M. B. Robinson J. R. Rogers

2003-01-01

215

Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets.  

PubMed

Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols. PMID:23862921

Uras-Aytemiz, Nevin; Devlin, J Paul

2013-07-14

216

Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets  

NASA Astrophysics Data System (ADS)

Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols.

Uras-Aytemiz, Nevin; Devlin, J. Paul

2013-07-01

217

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods. Dilatometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions.

Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

1999-01-01

218

Nonisothermal nucleation in the CuCl solid solution in glass: Formation of two distributions of nanoparticles of a new phase in the solid solution with a negative jump of the nucleation temperature  

NASA Astrophysics Data System (ADS)

The processes of nonisothermal nucleation in the CuCl solid solution in glass with a negative jump of the nucleation temperature have been investigated using optical spectroscopy and exciton-thermal analysis. Two distributions of CuCl nanoparticles differing in the average radii R (2.3 and 14.0 nm) have been obtained for the temperature drop from T 1 = 700°C to T 2 = 500°C. The formation of two distributions of CuCl particles has been numerically simulated and the agreement between the experimental and calculated radius distributions of CuCl particles has been obtained.

Leiman, V. I.; Valov, P. M.; Maksimov, V. M.; Derkacheva, O. Yu.; Markov, E. S.

2013-06-01

219

Gas-Liquid Flows and Phase Separation  

NASA Technical Reports Server (NTRS)

Common issues for space system designers include:Ability to Verify Performance in Normal Gravity prior to Deployment; System Stability; Phase Accumulation & Shedding; Phase Separation; Flow Distribution through Tees & Manifolds Boiling Crisis; Heat Transfer Coefficient; and Pressure Drop.The report concludes:Guidance similar to "A design that operates in a single phase is less complex than a design that has two-phase flow" is not always true considering the amount of effort spent on pressurizing, subcooling and phase separators to ensure single phase operation. While there is still much to learn about two-phase flow in reduced gravity, we have a good start. Focus now needs to be directed more towards system level problems .

McQuillen, John

2004-01-01

220

Nitrogen Removal from Natural Gas: Phase II.  

National Technical Information Service (NTIS)

SRI identified (bis)tricyclohexylphosphine molybdenum tricarbonyl as a candidate component in an absorption system for upgrading substandard natural gas to pipeline standards by removing nitrogen. The molybdenum compound reacted selectively with nitrogen ...

D. C. Bomberger J. L. Bomben A. Amirbahman M. Asaro

1999-01-01

221

Vacuum Gas Carburizing with Acetylene - Gas Phase Modeling of a Bench Scale Reactor  

Microsoft Academic Search

Vacuum gas carburizing is an important industrial process used for hardening the steel parts. The addition of carbon to the steel parts is accomplished by the pyrolysis of gaseous hydrocarbons. The gas phase composition is very important in vacuum gas carburizing to control the process. Pyrolysis of gaseous hydrocarbons is a complex process because of large number of reactions which

R. U. Khan; M. Saleem; A. Shafeeq

222

Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.  

ERIC Educational Resources Information Center

Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

Koury, Albert M.; Parcher, Jon F.

1979-01-01

223

Isospin lattice gas model and liquid-gas phase transition in asymmetric nuclear matter  

Microsoft Academic Search

Liquid-gas phase transition in asymmetric nuclear matter is investigated with an isospin lattice gas model. Nuclear matter is considered as a lattice with each lattice site either empty or occupied by a proton or a neutron, with a nearest-neighbor interaction between the nucleons. The Bragg-Williams mean field approximation is employed to evaluate the thermodynamic potential. Our model exhibits liquid-gas phase

S. Ray; J. Shamanna; T. T. S. Kuo

1997-01-01

224

Gas phase reaction of sulfur trioxide with water vapor  

Microsoft Academic Search

Sulfur trioxide (SO3) has long been known to react with water to produce sulfuric acid (H2S04). It has been commonly assumed that the gas phase reaction in the Earth`s atmosphere between SO3 and water vapor to produce sulfuric acid vapor is an important step in the production of sulfuric acid aerosol particles. The kinetics of the gas phase reaction of

C. E. Kolb; M. J. Molina; J. T. Jayne; R. F. Meads; D. R. Worsnop; A. A. Viggiano

1994-01-01

225

Freeze drying for gas chromatography stationary phase deposition  

Microsoft Academic Search

The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The

Sylwester; Alan P

2007-01-01

226

Reticulated vitreous carbon electrodes for gas phase pulsed corona reactors  

Microsoft Academic Search

A new design for gas phase pulsed corona reactors incorporating reticulated vitreous carbon (RVC) electrodes is demonstrated to be effective for the removal of nitrogen oxides from various gas mixtures containing O2, N2, water vapor and ethylene. The reactor consists of either a Plexiglass or glass cylindrical tube with macro-porous RVC electrodes placed perpendicularly to the cylinder axis. Streamers propagate

Michael Kirkpatrick; Wright C. Finney; Bruce R. Locke

2000-01-01

227

PRODUCTION OF VOID AND PRESSURE BY FISSION TRACK NUCLEATION OF RADIOLYTIC GAS BUBBLES DURING POWER BURSTS IN A SOLUTION REACTOR  

Microsoft Academic Search

The Kinetic Experiment on Water Boiler (KEWB) reactor is a 50-kw aqueous ;\\u000a homogeneous research reactor which was designed to study the safety ;\\u000a characteristics and dynamic behavior of this class of reactors. When the reactor ;\\u000a is placed on a short-period power transient, its aqueous uranyl sulfate fuel ;\\u000a solution becomes rapidly supersaturated with H gas produced by the

P. Spiegler; C. F. Jr. Bumpus; A. Norman

1962-01-01

228

Gas bubble nucleation and tritium permeation through metallic walls in a liquid 83Pb17Li blanket  

Microsoft Academic Search

Recent studies have given lower and lower values for the solubility of hydrogen isotopes in the eutectic 83Pb-17Li alloy, a candidate breeding material for the blanket of fusion machines. Therefore, thermodynamic stability for the gaseous phase under the high pressure reached at the bottom of the alloy containers can be achieved even for very low tritium concentrations in the liquid

R. Carta; S. Dernini; A. M. Polcaro; P. F. Ricci; G. Tola; G. Pierini

1989-01-01

229

High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations  

NASA Astrophysics Data System (ADS)

Our high resolution ion mobility apparatus has been modified by attaching an electrospray source to perform measurements for biological molecules. While the greater resolving power permits the resolution of more conformations for BPTI and cytochrome c, the resolved features are generally much broader than expected for a single rigid conformation. A major advantage of the new experimental configuration is the much gentler introduction of ions into the drift tube, so that the observed gas phase conformations appear to more closely reflect those present in solution. For example, it is possible to distinguish between the native state of cytochrome c and the methanol-denatured form on the basis of the ion mobility measurements; the mass spectra alone are not sensitive enough to detect this change. Thus this approach may provide a quick and sensitive tool for probing the solution phase conformations of biological molecules.

Hudgins, Robert R.; Woenckhaus, Jürgen; Jarrold, Martin F.

1997-11-01

230

Nucleation and growth of magnetite from solution  

NASA Astrophysics Data System (ADS)

The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite—a magnetic iron oxide with numerous bio- and nanotechnological applications—proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

Baumgartner, Jens; Dey, Archan; Bomans, Paul H. H.; Le Coadou, Cécile; Fratzl, Peter; Sommerdijk, Nico A. J. M.; Faivre, Damien

2013-04-01

231

Nucleation of electroactive ?-phase poly(vinilidene fluoride) with CoFe2O4 and NiFe2O4 nanofillers: a new method for the preparation of multiferroic nanocomposites  

NASA Astrophysics Data System (ADS)

Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials. In this paper we report on the nucleation of the electroactive ?-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe2O4 and NiFe2O4 nanoparticles in order to prepare poly(vinylidene fluoride)/ferrite nanocomposite for multiferroic and magnetoelectric applications,. The dispersed ferrite nanofiller particles strongly enhance the nucleation of the ?-phase of the polymer matrix. In this way, magnetoelectric polymer nanocomposites can be processed avoiding the usual ?- to ?-phase transformation by stretching of the polymer matrix.

Martins, P.; Costa, C. M.; Lanceros-Mendez, S.

2011-04-01

232

Gas phase precursors to anthropogenic secondary organic aerosol: detailed observations of 1,3,5-trimethylbenzene photooxidation  

NASA Astrophysics Data System (ADS)

A series of photooxidation experiments were conducted in an atmospheric simulation chamber in order to investigate the secondary organic aerosol (SOA) formed from the anthropogenic model gas phase precursor, 1,3,5-trimethylbenzene. Alongside specific aerosol measurements, comprehensive gas phase measurements, primarily by chemical ionisation reaction time-of-flight mass spectrometry (CIR-TOF-MS), were carried out to provide detailed insight into the composition and behaviour of the organic components of the gas phase matrix during SOA formation. An array of gas phase organic compounds was measured during the oxidation process, including several previously unmeasured primary bicyclic compounds possessing various functional groups. Analysis of results obtained during this study implies that these peroxide bicyclic species along with a series of furanones and organic acids contribute to SOA growth. The effect of varying the VOC/NOx ratio on SOA formation was explored, as was the effect of acid seeding. It was found that low NOx conditions favour more rapid aerosol formation and a higher aerosol yield, a finding that points towards a role for organic peroxides in the nucleation process and SOA growth.

Wyche, K. P.; Monks, P. S.; Ellis, A. M.; Cordell, R. L.; Parker, A. E.; Whyte, C.; Metzger, A.; Dommen, J.; Duplissy, J.; Prevot, A. S. H.; Baltensperger, U.; Rickard, A. R.; Wulfert, F.

2008-06-01

233

Vaccum Gas Tungsten Arc Welding, phase 1  

Microsoft Academic Search

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into

P. D. Krotz; D. T. Todd; Y. K. Liaw

1995-01-01

234

Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films  

SciTech Connect

We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.

Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter; Hellwig, Olav

2008-12-09

235

Nucleation Phenomena in Polymers.  

National Technical Information Service (NTIS)

The effects of nucleating agents on the physical strength properties of selected thermosetting polymer systems were experimentally investigated with emphasis on modified polyamides and specially synthesized ordered epoxy polymers. Nucleating agents such a...

W. Brenner R. F. Shaffer R. Vermes C. Marsel W. H. Kapfer

1968-01-01

236

A gas-phase solvent effect  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations at the CP-dG2thaw and MP2(thaw)/B4G levels of theory are reported for the bare HOMg+OCO ion resulting from addition of CO2 to HOMg+, and to its mono-, di- and tri-hydrated forms. These calculations are used to determine bond dissociation energy (BDE) values for the (H2O)n(CO2)iHOMg+-OH2 (n = 0-2; i = 0, 1) and (H2O)nHOMg+-OCO (n = 0-3) bonds, as well as to ascertain the relative energies for several key stationary points on each of the HOMg+·(H2O)n·CO2 (n = 0-3) potential energy surfaces. Three principal findings emerge from these calculations. First, in contrast to the isoelectronic system NaOH + CO2 --> NaO2COH held to play a leading role in noctilucent cloud nucleation, the reaction of HOMg+ + CO2 does not result in formation of the magnesium bicarbonate cation Mg+O2COH. Second, the cumulative Mg+-ligand bond energies for complexes of HOMg+ with several H2O and CO2 molecules rapidly approach, and then exceed, the available Mg+ recombination energy, indicating that dissociative recombination of HOMg+·(H2O)n·CO2 (or its bicarbonate-containing isomer Mg+O2COH·(H2O)n) is likely to result in the production of molecular Mg-containing neutrals. Third, we find that hydration exhibits a remarkable influence on the reactivity of HOMg+ with mesospheric CO2: addition of CO2 to bare HOMg+ does not result in bicarbonate formation, nor do the reactions of HOMg+·CO2 and HOMg+·OH2·CO2 with H2O, but the reaction of HOMg+·(OH2)2·CO2 with H2O leads to two possible bicarbonate-containing products (H2O)2·Mg+O2COH and (H2O)3·Mg+O2COH. The former product channel, which involves association followed by H2O loss, is judged to be an unusual example of a catalytic process in which the principal contribution of the H2O [`]catalyst' is steric.

Petrie, Simon

2006-08-01

237

Nucleation of lamellar domains from a sponge phase under shear flow: Shape selection of nuclei in a nonequilibrium steady state  

Microsoft Academic Search

It is a fundamental physical problem how a state is selected in a nonequilibrium steady state where the energy is continuously dissipated. This problem is common to phase transitions in liquids under shear flow and those in solids under deformation or electric current. In particular, soft matter often exhibits a strong nonlinear response to an external field, since its structural

Hideyuki Miyazawa; Hajime Tanaka

2007-01-01

238

Igniting homogeneous nucleation  

Microsoft Academic Search

Transient homogeneous nucleation is studied in the limit of large critical sizes. Starting from pure monomers, three eras of transient nucleation are characterized in the classic Becker-Döring kinetic equations with two different models of discrete diffusivity: the classic Turnbull-Fisher formula and an expression describing thermally driven growth of the nucleus. The latter diffusivity yields time lags for nucleation which are

J. C. Neu; L. L. Bonilla; A. Carpio

2005-01-01

239

Constant volume gas cell optical phase-shifter  

DOEpatents

A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.

Phillion, Donald W. (Dublin, CA)

2002-01-01

240

Molecular dynamics of simulation of the nucleation, growth, inhibition and control of gas hydrates. Annual report, March 1992-June 1993  

SciTech Connect

This is the second year of a three-year project using molecular simulation techniques tailored specifically for the determination of early-stage kinetics of natural gas hydrate crystal growth and dissolution. This year, extensive simulations of the kinetics of growth of a model system showed the appearance of magic numbers' in the growth rate versus cluster size. The feasibility of monitoring the kinetics of hydrate growth and dissolution has been demonstrated. A preliminary mechanism for hydrate dissolution has been proposed. A building block' for hydrate growth has been identified as a long-lived entity in the liquid; this single dodecahedron has also been seen by preliminary NMR studies. Inhibition studies have begun with biopolymers and will continue next year with studies of simple inhibitors, in concert with molecular spectroscopic techniques.

Clancy, P.

1993-06-01

241

Effect of Be on the nucleation and growth of beta' phase in aluminum-magnesium-silicon alloy  

Microsoft Academic Search

An investigation on the effect of Be on betasp' phase precipitation in Al-0.7%Mg-0.4%Si alloy was carried out using microhardness and resistivity measurements, and optical and TEM observations. It is shown that addition of 0.4%Be to an Al-0.7%Mg-0.4%Si (base) alloy significantly enhances the age hardening response and increases the peak hardness levels of the alloy, which is associated with a refinement

Ali Hatab

1997-01-01

242

Development and evaluation of the aerosol dynamic and gas phase chemistry model ADCHEM  

NASA Astrophysics Data System (ADS)

The aim of this work was to develop a model ideally suited for detailed studies on aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1×1 km2) to regional or global scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM), which has been developed and used at Lund University since 2007. The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions), which is not treated in Lagrangian box-models (0-space dimensions). The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others ideally suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The gas phase chemistry model calculates the gas phase concentrations of 63 different species, using 119 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malmö in Southern Sweden (280 000 inhabitants). Several sensitivity tests were performed concerning the number of size bins, size structure method, coupled or uncoupled condensation, the volatility basis set (VBS) or traditional 2-product model for secondary organic aerosol formation, different aerosol dynamic processes and vertical and horizontal mixing. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used between 1.5 and 2500 nm, while the moving-center method is preferable when only a few size bins are selected. The particle number size distribution in the center of the urban plume from Malmö is mainly affected by dry deposition, coagulation and condensation, and is relatively insensitive to moderate variations in the vertical and horizontal mixing, as long as the mixing height is relatively uniform. The modeled PM2.5 was dominated by organics, nitrate, sulfate and ammonium. If treating the condensation of HNO3 and NH3 as a coupled process (pH independent) the model gave lower nitrate PM2.5 values than if considering uncoupled condensation. However, both methods gave similar and significant temporal variation in the particulate nitrate content, primarily due to fluctuation in the relative humidity.

Roldin, P.; Swietlicki, E.; Schurgers, G.; Arneth, A.; Lehtinen, K. E. J.; Boy, M.; Kulmala, M.

2010-08-01

243

Development and evaluation of the aerosol dynamics and gas phase chemistry model ADCHEM  

NASA Astrophysics Data System (ADS)

The aim of this work was to develop a model suited for detailed studies of aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1 × 1 km2) to regional scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM). The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions). The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others well suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The organic mass partitioning was either modeled with a 2-dimensional volatility basis set (2D-VBS) or with the traditional two-product model approach. In ADCHEM these models consider the diffusion limited and particle size dependent condensation and evaporation of 110 and 40 different organic compounds respectively. The gas phase chemistry model calculates the gas phase concentrations of 61 different species, using 130 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malmö in southern Sweden (280 000 inhabitants). Several sensitivity tests were performed concerning the number of size bins, size structure method, aerosol dynamic processes, vertical and horizontal mixing, coupled or uncoupled condensation and the secondary organic aerosol formation. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used between 1.5 and 2500 nm, while the moving-center method is preferable when only a few size bins are selected. The particle number size distribution in the center of the urban plume from Malmö was mainly affected by dry deposition, coagulation and vertical dilution. The modeled PM2.5 mass was dominated by organic material, nitrate, sulfate and ammonium. If the condensation of HNO3 and NH3 was treated as a coupled process (pH independent) the model gave lower nitrate PM2.5 mass than if considering uncoupled condensation. Although the time of ageing from that SOA precursors are emitted until condensable products are formed is substantially different with the 2D-VBS and two product model, the models gave similar total organic mass concentrations.

Roldin, P.; Swietlicki, E.; Schurgers, G.; Arneth, A.; Lehtinen, K. E. J.; Boy, M.; Kulmala, M.

2011-06-01

244

Microfabricated Gas Phase Chemical Analysis Systems  

SciTech Connect

A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

Casalnuovo, Stephen A.; Frye-Mason, Gregory C; Heller, Edwin J.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carolyn M.; Wong, C. Channy

1999-08-02

245

Diffuse interface model of bulk heterogeneous nucleation  

SciTech Connect

First order phase transformations from a homogeneous initial state begin with nucleation, i.e. the new phase appears through heterophase fluctuations that are larger than a critical size which is determined by the interplay of the interfacial and volumetric contributions to the Gibbs free energy of the fluctuation. The heterogeneous process plays an essential role in determining the microstructure of solids. In materials science nucleation is usually described by a simple and flexible phenomenological model, the classical nucleation theory (CNT) which postulates that the nuclei are spherical particles characterized by the bulk properties of the nucleating phase and the bulk interfacial free energy [gamma] ('droplet' approximation). This simple picture is often criticized on the grounds that computer simulations and calculations from first principles predict an interface thickness comparable to the size of the nucleus. It is also alarming that for vapor condensation an the nucleation rates predicted by the CNT for crystal nucleation from melts or glasses is not feasible since in the undercooled state the solid/liquid interfacial free energy cannot be measured by independent methods. Nevertheless, the problems in interpreting experiments on bulk nucleation in terms of the CNT raise doubts about the validity of the classical approach. To circumvent these problems a simplified theory of homogeneous nucleation (DIT) that accounts for the diffuseness of the interface has been proposed recently. The new approach led to an improved description of vapor condensation and crystal nucleation from a glass. In the present work this model is generalized for the heterogeneous mechanism and compared to experiments on metallic substances. The results support the expectation that the DIT eliminates the problem of anomalous'' nucleation prefactors.

Granasy, L. (Research Inst. for Solid State Physics, Budapest (Hungary)); Egry, I.; Ratke, L.; Herlach, D.M. (DLR, Koeln (Germany). Institut fuer Raumsimulation)

1994-09-01

246

Fabrication and morphologies of large directly ordered L1{sub 0} FePt nanoparticles in gas phase  

SciTech Connect

Gas phase synthesis of large directly ordered L1{sub 0} FePt nanoparticles was studied. Simultaneous control of the chemical ordering and the size of the FePt nanoparticle was successfully achieved. It was found that the chemical ordering of the FePt nanoparticles was mainly influenced by the energy conditions (thermal environments at nucleation and growth regions), which could be adjusted by varying the process parameters including the sputtering current density, the Ar gas pressure, etc. The sizes of ordered FePt nanoparticles were more related to the Fe and Pt atoms' density at the initial stage (close to target surface). Multiply twinned structures were observed in L1{sub 0} FePt nanoparticles with 12 and 17 nm mean sizes, but were absent in L1{sub 0} FePt nanoparticles with 6 nm mean size, which caused the relatively low coercivity of large L1{sub 0} FePt nanoparticles.

Liu Xiaoqi; Wang Jianping [Center for Micromagnetics and Information Technologies (MINT) and Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

2009-04-01

247

Nucleation and growth of chemical vapor deposited diamond films  

NASA Astrophysics Data System (ADS)

This research involves a study of the nucleation and growth processes during diamond chemical vapor deposition (CVD) via numerical modeling and simulations. Numerical models have been developed: (1) to examine the chemistry of the intermediate layer that forms at the interface between diamond and non-diamond substrate, (2) to understand the nucleation, size and structure of diamond phase carbon clusters on Si(111) substrates, (3) to study the morphological instabilities associated with diamond growth during chemical vapor deposition. The chemistry of the intermediate layer that develops at the interface between diamond and non-diamond substrate during chemical vapor deposition is analyzed using a thermodynamic quasiequilibrium model. Substrates of Si, Mo, W, Ti, Ta, Fe and Ni are examined, and operating parameters such as the substrate temperature, reactor pressure, and CHsb4:Hsb2 ratio in the gas phase required for the growth of the respective metal carbides/solid carbon are predicted. It is shown that the quasiequilibrium approach is advantageous in that it minimizes the use of kinetics to the degree that rate expressions are obtained without requiring the knowledge of the detailed kinetic models of the processes. A theoretical study of the nucleation, size, and structure of diamond-phase carbon clusters on Si(111) substrates is presented. Silicon is chosen as the non-diamond substrate in this work as it is a common substrate material for diamond deposition. Molecular mechanics analysis has been utilized to predict energetically and entropically feasible pathways for nucleation of carbon clusters. Several mechanistic pathways for nucleation of carbon clusters are examined with Csb2Hsb2 and/or CHsb3 as the nucleation precursors. A possible model for the nucleation mechanism of diamond-phase carbon clusters on beta-SiC(111) surface, which forms epitaxially on Si(111) substrates, is presented. The critical size of the carbon clusters is calculated based on the atomistic theory of nucleation and the proposed nucleation mechanisms. The diamond CVD process has been examined theoretically and the morphological instabilities associated with the growth of diamond films have been investigated with a model based on the continuum species conservation equations coupled to surface reaction kinetics. An analytical model is developed to study the morphological instabilities of the diamond-gas interface during the diamond CVD process based on the linear and nonlinear perturbation theories. Linear stability analysis cannot be used to analyze the evolution of the unstable planar interface to a nonplanar cellular interface. Nonlinear analysis is carried out to study the growth behavior of an interface more accurately over a longer period of time. A two-dimensional numerical model describes the evolution of the gas-solid interface. The numerical and analytical models determine the critical parameters affecting the diamond deposition layer morphology. A dispersive relation is derived which relates the effects of species diffusive transport towards the growing interface, surface diffusion, surface tension, and geometrical factors with the stability of perturbations on the interface. (Abstract shortened by UMI.)

Mahalingam, Pushpa

248

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.

2003-01-01

249

Collision-induced gas phase dissociation rates  

NASA Technical Reports Server (NTRS)

The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

Hansen, C. Frederick

1990-01-01

250

Capillary gas chromatography with two new moderately high temperature phases.  

NASA Technical Reports Server (NTRS)

Gas chromatography test results are presented for two new moderately high-temperature phases of Dexsil 400-GC with free hydroxyl end groups (uncapped) and with end groups covered by trimethyl silyl groups (capped). The two Dexsil 400-GC phases were tested for their ability to resolve N-TFA-DL-(+)-2-butyl esters and n-butyl esters, as well as fatty acid methyl esters and hydrocarbon standards. Generally the more polar uncapped phase was superior to the capped phase in all separation comparisons, except for the hydrocarbons.

Pollock, G. E.

1972-01-01

251

Gas phase metal cluster model systems for heterogeneous catalysis.  

PubMed

Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed. PMID:22669249

Lang, Sandra M; Bernhardt, Thorsten M

2012-07-14

252

Specific and reproducible gas sensors utilizing gas-phase chemical reaction on organic transistors.  

PubMed

Utilizing a textbook reaction on the surface of an organic active channel, achieves sensitive detection of HCl, NH3 and NO2, with good selectivity, excellent reproducibility, and satisfactory stability. These results reveal gas-phase reaction assisted detection as a unique and promising approach to construct practical applicable gas sensors with typical organic transistors. PMID:24510689

Zang, Yaping; Zhang, Fengjiao; Huang, Dazhen; Di, Chong-an; Meng, Qing; Gao, Xike; Zhu, Daoben

2014-05-01

253

Gas phase hydrodynamics of a gas-solid turbulent fluidized bed reactor  

Microsoft Academic Search

Transient gas mixing tests in a gas-solid fluidized bed are analyzed with a dispersive plug flow model from the bubbling to the turbulent regime, and with the two-phase model of van Deemter. It is shown that dispersion fluctuations can also be used besides pressure fluctuations or capacitance probes to characterize the transition between the bubbling and the turbulent regime. Furthermore,

M. Foka; J. Chaouki; C. Guy; D. Klvana

1996-01-01

254

Freeze drying for gas chromatography stationary phase deposition  

DOEpatents

The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

Sylwester, Alan P. (Livermore, CA)

2007-01-02

255

Improved coarse-grained model for molecular-dynamics simulations of water nucleation.  

PubMed

We developed a new coarse-grained (CG) model for water to study nucleation of droplets from the vapor phase. The resulting potential has a more flexible functional form and a longer range cutoff compared to other CG potentials available for water. This allowed us to extend the range of applicability of coarse-grained techniques to nucleation phenomena. By improving the description of the interactions between water molecules in the gas phase, we obtained CG model that gives similar results than the all-atom (AA) TIP4P model but at a lower computational cost. In this work we present the validation of the potential and its application to the study of nucleation of water droplets from the supersaturated vapor phase via molecular-dynamics simulations. The computed nucleation rates at T = 320 K and 350 K at different supersaturations, ranging from 5 to 15, compare very well with AA TIP4P simulations and show the right dependence on the temperature compared with available experimental data. To help comparison with the experiments, we explored in detail the different ways to control the temperature and the effects on nucleation. PMID:24028121

Zipoli, Federico; Laino, Teodoro; Stolz, Steffen; Martin, Elyette; Winkelmann, Christoph; Curioni, Alessandro

2013-09-01

256

Stochastic Lindemann kinetics for unimolecular gas-phase reactions.  

PubMed

Lindemann, almost a century ago, proposed a schematic mechanism for unimolecular gas-phase reactions. Here, we present a new semiempirical method to calculate the effective rate constant in unimolecular gas-phase kinetics through a stochastic reformulation of Lindemann kinetics. Considering the rate constants for excitation and de-excitation steps in the Lindemann mechanism as temperature dependent empirical parameters, we construct and solve a chemical master equation for unimolecular gas-phase kinetics. The effective rate constant thus obtained shows excellent agreement with experimental data in the entire concentration range in which it is reported. The extrapolated values of the effective rate constant for very low and very high concentrations of inert gas molecules are in close agreement with values obtained using the Troe semiempirical method. Stochastic Lindemann kinetics, thus, provides a simple method to construct the full falloff curves and can be used as an alternative to the Troe semiempirical method of kinetic data analysis for unimolecular gas-phase reactions. PMID:23879409

Saha, Soma; Dua, Arti

2013-08-22

257

Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold  

NASA Astrophysics Data System (ADS)

Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd+ in the gas phase. While a lysozyme-Au adduct forms Au18+, Au25+, Au38+ and Au102+ ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag+, Pt2+, Pd2+, Cu2+, Fe2+, Ni2+ and Cr3+) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38+. While other metal ions like Cu2+ help forming Au25+ selectively, Fe2+ catalyzes the formation of Au25+ over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution.Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd+ in the gas phase. While a lysozyme-Au adduct forms Au18+, Au25+, Au38+ and Au102+ ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag+, Pt2+, Pd2+, Cu2+, Fe2+, Ni2+ and Cr3+) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38+. While other metal ions like Cu2+ help forming Au25+ selectively, Fe2+ catalyzes the formation of Au25+ over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr04257j

Baksi, Ananya; Pradeep, T.

2013-11-01

258

Femtosecond spectroscopy of cluster anions: insights into condensed-phase phenomena from the gas-phase.  

PubMed

Ultrafast spectroscopy allows chemical and physical processes to be observed on time-scales faster than the nuclear motion within molecules. This tutorial review explores how such experiments, and specifically time-resolved photoelectron spectroscopy on gas-phase cluster anions, provide a molecular-level understanding of the processes that are normally associated with condensed-phase dynamics. PMID:18224260

Verlet, Jan R R

2008-03-01

259

On chip steady liquid-gas phase separation for flexible generation of dissolved gas concentration gradient.  

PubMed

In this study, steady liquid-gas phase separation is realized by applying a hydrophobic small microchannel array (SMA) to bridge two large microchannels, one for liquid phase and one for gas phase. In this structure, a capillary pressure difference between that in the SMA and the larger channel results in a steady liquid-gas interface. The generated liquid-gas interface allows for fast gas dissolving speed. By coupling the liquid-gas interface with a one directional fluidic field, a steady dissolved gas concentration gradient (DgCG) is generated. The DgCG distribution is easily designable for linear or exponential modes, providing improved flexibility for gas participated processes on chip. To demonstrate its applicability, a CO(2) DgCG chip is fabricated and applied for screening CaCO(3) crystal growth conditions in the DgCG chip. Crystals with transitional structures are successfully fabricated, which is consistent with the CO(2) DgCG distribution. PMID:22336913

Xu, Bi-Yi; Hu, Shan-Wen; Yan, Xiao-Na; Xia, Xing-Hua; Xu, Jing-Juan; Chen, Hong-Yuan

2012-04-01

260

Fortran program sizes two-phase oil\\/gas separators  

Microsoft Academic Search

A Fortran program sizing two-phase oil\\/gas separators has been developed. The program is set up to provide a series of output results that can assist in designing and selecting surface production separators. It eliminates the use of charts and cuts down on lengthy calculations. The output results of the program include two sets of data, one for the vertical separators

M. S. Bizanti; Y. Hancheng

1987-01-01

261

Laboratory spectra of gas-phase coronene at elevated temperatures  

NASA Technical Reports Server (NTRS)

Gas-phase infrared spectra of coronene from 4000 to 400/cm are presented in emission and absorption at temperatures from 350 to 450 C. Peak positions are compared to KBr pellet data and to a previously published neon matrix-isolated coronene spectrum. Relative feature strengths are analyzed and used to estimate a temperature of interstellar PAHs assuming thermal emission.

Kurtz, J.

1992-01-01

262

Selected Examples of Gas-Phase Ion Chemistry Studies  

PubMed Central

Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Tröger bases having chiral nitrogen centers.

Nibbering, Nico M. M.

2013-01-01

263

LOW COST IMAGER FOR POLLUTANT GAS LEAK DETECTION - PHASE II  

EPA Science Inventory

An inexpensive imaging Instrument to quickly locate leaks of methane and other greenhouse and VOC gases would reduce the cost and effort expended by industry to comply with EPA regulations. In Phase I, of this WBIR program, a new gas leak visualization camera was demonstrated...

264

Fragment production and the liquid-gas phase transition  

SciTech Connect

An inclusive experiment in which isotopically resolved fragments, 3less than or equal toZless than or equal to13, were produced in high energy proton-nucleus collisions has provided evidence for a liquid-gas phase transition in nuclei. We review briefly the data and its description in terms of a critical phenomenon.

Hirsch, A.S.

1984-11-15

265

Ion-Molecule Reactions in Gas Phase Radiation Chemistry.  

ERIC Educational Resources Information Center

Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

Willis, Clive

1981-01-01

266

Negatively-charged helices in the gas phase.  

PubMed

A polyalanine-based peptide which forms a stable, negatively-charged ?-helix in the gas phase is reported. Addition of an N-terminal acidic residue forms a stabilizing hydrogen bond network and an electrostatic interaction with the helical dipole. Formation of this secondary structure was demonstrated using ion mobility-mass spectrometry and molecular modelling techniques. PMID:24901462

Johnson, Andrew R; Dilger, Jonathan M; Glover, Matthew S; Clemmer, David E; Carlson, Erin E

2014-07-15

267

Statistical and Microscopic Approach to Gas Phase Chemical Kinetics.  

ERIC Educational Resources Information Center

Describes advanced undergraduate laboratory exercise examining the dependence of the rate constants and the instantaneous concentrations with the nature and energy content in a gas-phase complex reaction. Computer program (with instructions and computation flow charts) used with the exercise is available from the author. (Author/JN)

Perez, J. M.; Quereda, R.

1983-01-01

268

Formation and dissociation processes of gas-phase detergent micelles.  

PubMed

Growing interest in micelles to protect membrane complexes during the transition from solution to gas phase prompts a better understanding of their properties. We have used ion mobility mass spectrometry to separate and assign detergent clusters formed from the n-trimethylammonium bromide series of detergents. We show that cluster size is independent of detergent concentration in solution, increases with charge state, but surprisingly decreases with alkyl chain length. This relationship contradicts the thermodynamics of micelle formation in solution. However, the liquid drop model, which considers both the surface energy and charge, correlates extremely well with the experimental cluster size. To explore further the properties of gas-phase micelles, we have performed collision-induced dissociation on them during tandem mass spectrometry. We observed both sequential asymmetric charge separation and neutral evaporation from the precursor ion cluster. Interestingly, however, we also found markedly different dissociation pathways for the longer alkyl chain detergents, with significantly fewer intermediate ions formed than for those with a shorter alkyl chain. These experiments provide an essential foundation for understanding the process of the gas-phase analysis of membrane protein complexes. Moreover they imply valuable mechanistic details of the protection afforded to protein complexes by detergent clusters during gas-phase activation processes. PMID:22512598

Borysik, Antoni J; Robinson, Carol V

2012-05-01

269

First measurements of gas phase sulphuric acid in the stratosphere  

Microsoft Academic Search

Measurements of the abundance of gas phase sulfuric acid in the stratosphere are reported. Compositions and abundances of stratospheric negative ions were observed at an altitude of 36.5 km, and the presence of species containing sulfuric acid molecules attached to HSO4(-) core ions was detected. A proposed reaction scheme suggests that the cores of these ions are formed by reactions

F. Arnold; R. Fabian

1980-01-01

270

Evaluated Chemical Kinetic Rate Constants for Various Gas Phase Reactions  

Microsoft Academic Search

The available information, up to mid-1972, for the rate constants of a series of gas phase chemical reactions has been evaluated critically. For each reaction, relevant thermodynamic data are presented and values for the equilibrium constant expressed in mathematical form. Kinetic data are presented in tabular and graphical form together with a discussion of the pertinent details. Recommended rate constant

Keith Schofield

1973-01-01

271

Reticulated vitreous carbon electrodes for gas phase pulsed corona reactors  

Microsoft Academic Search

A new design for gas phase pulsed corona reactors incorporating reticulated vitreous carbon electrodes is demonstrated to be effective for the removal of nitrogen oxides from synthetic air mixtures. The reactor consists of a plexiglass tube with porous reticulated carbon disk electrodes placed perpendicularly to the cylinder axis. Streamers propagate between the reticulated carbon disks providing a uniform exposure of

B. R. Looke; M. Kirkpatrick; H. Hanson; W. C. Finney

1998-01-01

272

Optically-Based Diagnostics for Gas-Phase Laser Development.  

National Technical Information Service (NTIS)

In this paper we describe several diagnostics that we have developed to assist the development of high power gas phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements of O2(a), small signal gain, iodi...

A. J. Hicks K. L. Galbally-Kinney S. Lee W. J. Kessler W. T. Rawlins

2010-01-01

273

Optically based diagnostics for gas-phase laser development  

Microsoft Academic Search

In this paper we describe several diagnostics that we have developed to assist the development of high power gas phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements of O2(a), small signal gain, iodine dissociation, and temperature. These are key operational parameters within COIL, and these diagnostics have been used world-wide to gain

Wilson T. Rawlins; Seonkyung Lee; Kristin L. Galbally-Kinney; William J. Kessler; Adam J. Hicks; Ian M. Konen; Emily P. Plumb; Steven J. Davis

2010-01-01

274

Electron diffraction studies of supersonic jets. 8. Nucleation of various phases of SF/sub 6/, SeF/sub 6/, and TeF/sub 6/  

SciTech Connect

Old microcrystals of SF/sub 6/, SeF/sub 6/, and TeF/sup 6/ are condensed when the gaseous hexafluorides in monatomic carriers flow supersonically through aminiature Laval nozzle. Electron diffraction records of the condensates display strong Debye-Scherrer rings. The diffraction patterns depend markedly upon the carrier gas and expansion conditions. For the hexafluorides of sulfur and selenium the well-known body-centered plastic cubic phase forms if the molecular weight of the carrier gas is low and the subject mole fraction exceeds several percent. A phase II of low symmetry begins to appear only at low mole fractions of SF/sub 6/ and requires a carrier at least has heavy as argon. Phase II appears for SeF/sub 6/ with argon carrier under all conditions examined and with neon under extreme conditions. It appears readily even with helium in the case of TeF/sub 6/, provided the subject mole fraction is comparatively high. At lower mole fractions and total pressures another, as yet unidentified, phase III of TeF/sub 6/ is produced. Patterns of phase II are well accounted for by the triclinic lattice P1, Z = 3. Refinements based on this space group, for the two compounds yielding nearly pure phase II, led to the following cell constants (3sigma): SeF/sub 6/ (T < 140 K), a = 14.51 (8) A, b = 8.22 (3) A, c = 4.92 (3) A, ..cap alpha.. = 85.6 (3)/sup 0/; ..beta.. = 93.7 (4)/sup 0/, ..gamma.. = 88.14 (4)/sup 0/; TeF/sub 6/ (T < 160 K.), a = 14.99 (7) A, b = 8.53 (3) A, c = 5.06 (3) A, ..cap alpha.. = 85.6 (3)/sup 0/, ..beta.. = 93.5 (3)/sup 0/ = 88.9 (3)/sup 0/.

Bartell, L.S.; Valente, E.J.; Caillat, J.C.

1987-05-07

275

Star formation via the phase transition of an adiabatic gas  

NASA Technical Reports Server (NTRS)

An analytic model based on a second-order accurate global virial analysis is used to describe two stable equilibrium states for rotating gas clouds: a pressure-supported, diffuse state and a rotationally supported, compact state. Diffuse and compact equilibrium sequences are identified along which slow, secular evolution of a gas cloud can occur. A virial analysis provides analytic expressions for the limiting masses of gas clouds at points of dynamical instability. The minimum mass below which external triggers of any amplitude cannot effectively induce star formation is identified for adiabatic gas clouds. It is suggested that fluctuations in the ISM of some galaxies may actually cause star formation to proceed primarily via a phase transition, rather than via the classical Jeans instability.

Tohline, Joel E.; Christodoulou, Dimitris M.

1988-01-01

276

Diamond nucleation using polyethene  

DOEpatents

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

2013-07-23

277

The Vacuum Bubble Nucleation  

SciTech Connect

We study the nucleation of a vacuum bubble via the vacuum-to-vacuum tunneling transition in curved spacetime. We consider Coleman-de Luccia's semiclassical approximation at zero temperature in pure Einstein theory of gravity and the theory with nonminimal coupling. We discuss the dynamics of a nucleated vacuum bubble.

Lee, Bum-Hoon [Department of Physics and Center for Quantum Spacetime, Sogang University Seoul 121-742 (Korea, Republic of); Lee, Wonwoo [Center for Quantum Spacetime, Sogang University, Seoul 121-742 (Korea, Republic of)

2009-07-10

278

Gas phase decontamination of gaseous diffusion process equipment  

SciTech Connect

D&D of the process facilities at the gaseous diffusion plants (GDPs) will be an enormous task. The EBASCO estimate places the cost of D&D of the GDP at the K-25 Site at approximately $7.5 billion. Of this sum, nearly $4 billion is associated with the construction and operation of decontamination facilities and the dismantlement and transport of contaminated process equipment to these facilities. In situ long-term low-temperature (LTLT) gas phase decontamination is being developed and demonstrated at the K-25 site as a technology that has the potential to substantially lower these costs while reducing criticality and safeguards concerns and worker exposure to hazardous and radioactive materials. The objective of gas phase decontamination is to employ a gaseous reagent to fluorinate nonvolatile uranium deposits to form volatile LJF6, which can be recovered by chemical trapping or freezing. The LTLT process permits the decontamination of the inside of gas-tight GDP process equipment at room temperature by substituting a long exposure to subatmospheric C1F for higher reaction rates at higher temperatures. This paper outlines the concept for applying LTLT gas phase decontamination, reports encouraging laboratory experiments, and presents the status of the design of a prototype mobile system. Plans for demonstrating the LTLT process on full-size gaseous diffusion equipment are also outlined briefly.

Bundy, R.D.; Munday, E.B.; Simmons, D.W.; Neiswander, D.W.

1994-03-01

279

Zinc Nucleation and Growth in Microgravity  

NASA Technical Reports Server (NTRS)

We report our experiences with zinc nucleation in a microgravity environment aboard NASA's Reduced Gravity Research Facility. Zinc vapor is produced by a heater in a vacuum chamber containing argon gas. Nucleation is induced by cooling and its onset is easily detected visually by the appearance of a cloud of solid, at least partially crystalline zinc particles. Size distribution of these particles is monitored in situ by photon correlation spectroscopy. Samples of particles are also extracted for later analysis by SEM. The initially rapid increase in particle size is followed by a slower period of growth. We apply Scaled Nucleation Theory to our data and find that the derived critical temperature of zinc, the critical cluster size at nucleation, and the surface tension values are all in reasonably good agreement with their accepted literature values.

Michael, B. Patrick; Nuth, J. A., III; Lilleleht, L. U.; Vondrak, Richard R. (Technical Monitor)

2000-01-01

280

Preconceptual design of the gas-phase decontamination demonstration cart  

SciTech Connect

Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker exposure to radioactive materials, and reduce safeguard concerns. This report documents the preconceptual design of the process equipment that is necessary to conduct a full-scale demonstration of the LTLT method in accordance with the process steps listed above. The process equipment and method proposed in this report are not intended to represent a full-scale production campaign design and operation, since the gas evacuation, gas charging, and off-gas handling systems that would be cost effective in a production campaign are not cost effective for a first-time demonstration. However, the design presented here is expected to be applicable to special decontamination projects beyond the demonstration, which could include the Deposit Recovery Program. The equipment will therefore be sized to a 200 ft size 1 converter (plus a substantial conservative design margin), which is the largest item of interest for gas phase decontamination in the Deposit Recovery Program. The decontamination equipment will allow recovery of the UF{sub 6}, which is generated from the reaction of ClF{sub 3} with the uranium deposits, by use of NaF traps.

Munday, E.B.

1993-12-01

281

Nucleate Boiling and the Chen Correlation for Flow Boiling Heat Transfer  

Microsoft Academic Search

In flow boiling experiments on water in a vertical tube, the Chen correlation predicted the convective heat transfer coefficient satisfactorily but overpredicted the nucleate boiling contribution. The tube material had rather low densities of bubble nucleation sites, measured by observation in boiling and by gas bubble nucleation: the methods agreed only if the gas measurements were made after boiling, which

Y. Aounallah; D. B. R. Kenning

1987-01-01

282

Heterogeneous nucleation in solutions: Generalized Gibbs' approach.  

PubMed

Heterogeneous nucleation in solutions on planar solid surfaces is modeled taking into account changes of the state parameters of the critical clusters in dependence on supersaturation. The account of the variation of the state parameters of the cluster phase on nucleation is performed in the framework of the generalized Gibbs' approach. A regular solution is chosen as a model for the analysis of the basic qualitative characteristics of the process. It is shown that, employing the generalized Gibbs approach, contact angle and catalytic activity factor for heterogeneous nucleation become dependent on the degree of metastability (supersaturation) of the solution. For the case of formation of a cluster in supersaturated solutions on a surface of low wettability (the macroscopic equilibrium contact angles being larger than 90°), the solid surface has only a minor influence on nucleation. In the alternative case of high wettability (for macroscopic equilibrium contact angles being less than 90°), nucleation is significantly enhanced by the solid surface. Effectively, the existence of the solid surface results in a significant shift of the spinodal to lower supersaturations as compared with homogeneous nucleation. Qualitatively, the same behavior is observed now near the new (solid surface induced) limits of instability of the solution as compared with the behavior near to the spinodal curve in the case of homogeneous nucleation. PMID:24985667

Abyzov, Alexander S; Schmelzer, Jürn W P

2014-06-28

283

Phase separation of a multiple occupancy lattice gas  

NASA Astrophysics Data System (ADS)

A binary lattice gas model that allows for multiple occupancy of lattice sites, inspired by recent coarse-grained descriptions of solutions of interacting polymers, is investigated by combining the steepest descent approximation with an exploration of the multidimensional energy landscape and by Gibbs ensemble Monte Carlo simulations. The one-component version of the model, involving on site and nearest-neighbour interactions, is shown to exhibit microphase separation into two sub-lattices with different mean occupation numbers. The symmetric two-component version of the multiple occupancy lattice gas is shown to exhibit a demixing transition into two phases above a critical mean occupation number.

Finken, Reimar; Hansen, Jean-Pierre; Louis, Ard A.

2004-01-01

284

Gas-liquid chromatography with a volatile "stationary" liquid phase.  

PubMed

A unique type of gas-liquid chromatography is described in which both mobile and "stationary" phases are composed of synthetic mixtures of helium and carbon dioxide. At temperatures below the critical point of the binary mixture and pressures above the vapor pressure of pure liquid carbon dioxide, helium and carbon dioxide can form two immiscible phases over extended composition ranges. A binary vapor phase enriched in helium can act as the mobile phase for chromatographic separations, whereas a CO2-rich liquid in equilibrium with the vapor phase, but condensed on the column wall, can act as a pseudostationary phase. Several examples of chromatographic separations obtained in "empty" capillary columns with no ordinary stationary liquid phase illustrate the range of conditions that produce such separations. In addition, several experiments are reported that confirm the proposed two-phase hypothesis. The possible consequences of the observed chromatographic phenomenon in the field of supercritical fluid chromatography with helium headspace carbon dioxide are discussed. PMID:12033313

Wells, P S; Zhou, S; Parcher, J F

2002-05-01

285

Efimov-driven phase transitions of the unitary Bose gas  

NASA Astrophysics Data System (ADS)

Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of ‘unitary’ interactions, where Efimov trimers form, is now accessible in cold-atom experiments. Here we use a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose–Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.

Piatecki, Swann; Krauth, Werner

2014-03-01

286

Chemistry inside molecular containers in the gas phase.  

PubMed

Inner-phase chemical reactions of guest molecules encapsulated in a macromolecular cavity give fundamental insight into the relative stabilization of transition states by the surrounding walls of the host, thereby modelling the situation of substrates in enzymatic binding pockets. Although in solution several examples of inner-phase reactions are known, the use of cucurbiturils as macrocyclic hosts and bicyclic azoalkanes as guests has now enabled a systematic mass spectrometric investigation of inner-phase reactions in the gas phase, where typically the supply of thermal energy results in dissociation of the supramolecular host-guest assembly. The results reveal a sensitive interplay in which attractive and repulsive van der Waals interactions between the differently sized hosts and guests need to be balanced with a constrictive binding to allow thermally activated chemical reactions to compete with dissociation. The results are important for the understanding of supramolecular reactivity and have implications for catalysis. PMID:23609087

Lee, Tung-Chun; Kalenius, Elina; Lazar, Alexandra I; Assaf, Khaleel I; Kuhnert, Nikolai; Grün, Christian H; Jänis, Janne; Scherman, Oren A; Nau, Werner M

2013-05-01

287

Bubble nucleation dynamics in 3He/4He mixture by holographic interferometry  

NASA Astrophysics Data System (ADS)

We were able to nucleate a gas bubble in the diluted phase of 3He-4He mixture by a 1 ms width strong sound pulse. The nucleated bubble became large and detached from the bottom transducer and was pushed out to the bulk liquid by the acoustic wave pulse. The bubble then repeatedly expanded and contracted a few times and finally disappeared. The overall motion of the bubble was traced by a high speed camera with a time resolution of 1 ms. We are attempting to investigate the small density fluctuation around the bubble by incorporating holographic interferometry technology. The measurement was done at T=0.35 K for the phase separated mixture at saturated vapor pressure. An acoustic wave transducer was located at the bottom of the cell, so the bubble was nucleated in the dilute phase of the mixture. We resolved the density fluctuation as small as ??/? = 2 × 10-6 in the dilute phase with the sample width of 25 mm, which could not be obtained by other methods. It was found that there appeared a less dense region of —??/? approx 1.46 × 10-3 just above the bubble. The bubble appeared just after the pulse was turned off, but this less dense region appeared prior to the emergence of the bulk bubble. It should be an important information about the bubble nucleation mechanism. This very high sensitivity of holographic interferometry with respect to the density fluctuation could be widely used in quantum liquid.

Morikawa, M.; Abe, H.; Nomura, R.; Okuda, Y.

2009-02-01

288

Effect of electron factor (number of electron holes) on kinetics of nucleation, growth, and dissolution of phases during long-term high-temperature holdings of 0.45C-26Cr-33Ni-2Si-2Nb superalloy  

NASA Astrophysics Data System (ADS)

The mechanism of phase transformations that occur in the structure and changes in the phase composition of the cast 0.45C-26Cr-33Ni-2Si-2Nb superalloy held at a temperature of 1150°C for times of up to 100 h have been explained based on a computerized theoretical analysis of the results of experimental investigations. It has been shown that the factor that determines the direction of the process of transformation of the structure (nucleation, growth, and dissolution of various phases) in Fe-Cr-Ni-based alloys during long-term high-temperature holdings is the number of electron holes in the electron shells of chemical elements and the phases they form. Kinetically, the process is limited by the diffusion of a substitutional element with a greatest ratio of its concentration in the new phase to that in the matrix ( C ph/ C 0).

Rudskoi, A. I.; Anastasiadi, G. P.; Kondrat'ev, S. Yu.; Oryshchenko, A. S.; Fuks, M. D.

2014-01-01

289

Determining the nucleation rate from the dimer growth probability.  

PubMed

A new method is proposed for the determination of the stationary one-component nucleation rate J with the help of data for the growth probability P2 of a dimer which is the smallest cluster of the nucleating phase. The method is based on an exact formula relating J and P2, and is readily applicable to computer simulations of nucleation. Using the method, the dependence of J on the supersaturation s is determined by kinetic Monte Carlo simulations of two-dimensional (2D) nucleation of monolayers on the (100) face of Kossel crystal. The change of J over nearly 11 orders of magnitude is followed and it is found that the classical nucleation theory overestimates the simulation J values by an s-dependent factor. The 2D nucleus size evaluated via the nucleation theorem is described satisfactorily by the classical Gibbs-Thomson equation and its corrected version accounting for the spinodal limit of 2D nucleation. PMID:16392573

ter Horst, Joop H; Kashchiev, Dimo

2005-09-15

290

The organic matter of Comet Halley as inferred by joint gas phase and solid phase analyses  

NASA Astrophysics Data System (ADS)

During encounters with Comet Halley, the experiment PICCA onboard Giotto measured the gas-phase organic ion composition of the coma, and the experiment PUMA onboard Vega-1 measured the dust composition. Joining both results gives a consistent picture of the parent organic matter from which dust and gas is produced: a complex unsaturated polycondensate, which splits during coma formation into the more refractory C=C,C-N-containing dust part and the more volatile C=C,C-O-containing gas part. The responsible exothermal chemical reactions, which are triggered by sunlight, may play a major role in the dynamics of coma formation.

Krueger, F. R.; Korth, A.; Kissel, J.

1991-04-01

291

Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: Ab initio simulations supporting center nucleation  

NASA Astrophysics Data System (ADS)

High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 ?m/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10-9 m2/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.

André, Yamina; Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Cadiz, Fabian; Rowe, Alistair; Paget, Daniel; Petit, Elodie; Leroux, Christine; Trassoudaine, Agnès; Réda Ramdani, M.; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne

2014-05-01

292

Substituent effects on the gas-phase acidity of silane  

SciTech Connect

In a previous paper, the gas-phase acidities of XH{sub n} compounds (X = C, N, O, F, Si, P, S, Cl) were predicted with ab initio wave functions. At the MP4{sup 2} level of theory with extended basis sets acidities for these species were determined to be within 2 kcal/mol of experimental value. In the present work, with 6-31G(d) geometries and full MP4/MC-311++G{sup 6}(3df,2pd) energies, the effects of CH{sub 3}, NH{sub 2}, OH, F, SiH{sub 3}, PH{sub 2}, SH, and Cl on the gas-phase acidity of silane are examined. Only a few related calculations have been carried out. All calculations were performed with Gaussian86, and all structures were verified as minima by diagonalizing the analytically determined hessians. Only the valence electrons were correlated in the perturbation theory calculations.

Gordon, M.S.; Volk, D.E. (North Dakota State Univ., Fargo (USA)); Gano, D.R. (Minot State Univ., ND (USA))

1989-12-20

293

Gas phase dynamics of triplet formation in benzophenone.  

PubMed

Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0. We have found that the triplet formation can be described almost as a direct process in preparing T1, the lowest reacting triplet state, from the S1 state after S2 ? S1 internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution. PMID:24728443

Spighi, Gloria; Gaveau, Marc-André; Mestdagh, Jean-Michel; Poisson, Lionel; Soep, Benoît

2014-04-23

294

Pr:YAG temperature imaging in gas-phase flows  

NASA Astrophysics Data System (ADS)

In this study, a new thermographic phosphor for planar gas-phase thermometry is investigated. The thermographic phosphor used is composed of trivalent praseodymium (Pr3+) ions doped into a yttrium aluminum garnet (YAG) host. Spectrally-resolved emission data were taken in a furnace for temperatures up to 1,300 K. The emission spectra were used to develop a temperature measurement strategy utilizing a non-equilibrium population ratio. The developed temperature measurement technique was demonstrated in a turbulent heated air jet for exit temperatures ranging from 300 to 750 K. The results demonstrate the promise of the Pr:YAG phosphor for obtaining high-precision single-shot temperature measurements in gas-phase flows.

Jordan, Jonathan; Rothamer, David A.

2013-03-01

295

Gas-phase reactivity of ruthenium carbonyl cluster anions  

Microsoft Academic Search

Partially-ligated anionic ruthenium carbonyl clusters react with alkenes, arenes, and alkanes in the gas phase; the products\\u000a undergo extensive C-H activation and lose dihydrogen and carbon monoxide under collision-induced dissociation conditions.\\u000a Triethylsilane and phenylsilane are also reactive towards the unsaturated clusters, and oxygen was shown to rapidly break\\u000a down the cluster core by oxidative cleavage of the metal-metal bonds. These

Matthew A. Henderson; Samantha Kwok; J. Scott McIndoe

2009-01-01

296

Statics and dynamics of phase segregation in multicomponent fermion gas  

Microsoft Academic Search

:   We investigate the statics and dynamics of spatial phase segregation process of a mixture of fermion atoms in a harmonic trap\\u000a using the density functional theory. The kinetic energy of the fermion gas is written in terms of the density and its gradients.\\u000a Several cases have been studied by neglecting the gradient terms (the Thomas-Fermi limit) which are then

K. Esfarjani; S. T. Chui; V. Kumar; Y. Kamazoe

2002-01-01

297

Photodissociation pathways of gas-phase photoactive yellow protein chromophores  

NASA Astrophysics Data System (ADS)

The absorption dynamics of two model chromophores of the photoactive yellow protein were studied in gas-phase experiments. Using different time-resolving techniques with an overall sensitivity ranging from seconds down to a few nanoseconds, complex dynamics were revealed for the p -coumaric acid anion, involving both fragmentation and electron detachment as possible photoresponse channels. For the trans-thiophenyl- p -coumarate model, despite its more complex molecular structure, simpler decay dynamics showing only fragmentation were observed.

Lammich, Lutz; Rajput, Jyoti; Andersen, Lars H.

2008-11-01

298

Correlated random-phase-approximation study of an anyon gas  

Microsoft Academic Search

The correlated random-phase-approximation (CRPA) method is applied to study the ground-state and excited-state properties of an anyon gas. We perform a systematic 1\\/{ital N} expansion to the calculation of elementary excitations, where {ital N} is the statistical parameter. We find that the leading-(1\\/{ital N})-order contributions are the same as those obtained by calculations of the RPA response functions. We then

B. H. Liu; X. Q. Wang; L. McLerran

1991-01-01

299

Correlated random-phase-approximation study of an anyon gas  

Microsoft Academic Search

The correlated random-phase-approximation (CRPA) method is applied to study the ground-state and excited-state properties of an anyon gas. We perform a systematic 1\\/N expansion to the calculation of elementary excitations, where N is the statistical parameter. We find that the leading-(1\\/N)-order contributions are the same as those obtained by calculations of the RPA response functions. We then consider corrections to

B. H. Liu; X. Q. Wang; L. McLerran

1991-01-01

300

Micro-structured reactors for gas phase reactions  

Microsoft Academic Search

This paper deals with reviewing on the application of micro-structured reactors for heterogeneously catalysed gas phase reactions. After a brief introduction covering some estimation criteria for the performance of micro-structured reactors, an overview of the work performed to date in the field is given. The reactors are classified by the type of catalyst applied (porous or non-porous) and according to

Gunther Kolb; Volker Hessel

2004-01-01

301

Gas phase fractionation method using porous ceramic membrane  

DOEpatents

Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)

1996-01-01

302

Femtosecond analysis of free molecular rotation in the gas phase  

NASA Astrophysics Data System (ADS)

The time-resolved S 1?S *n absorption anisotropy decay resulting from rotation of free gas phase POPOP molecules at 593 K and PPO molecules at 483 K was studied after S 0?S *1 excitation by femtosecond linearly polarized pulses at 308 nm. The time evolution of the anisotropy measured through a few picoseconds after excitation is in agreement with the results of calculations made for POPOP and PPO using orientational correlation functions developed for rigid asymmetric top molecules.

Borisevich, N. A.; Khoroshilov, E. V.; Kryukov, I. V.; Kryukov, P. G.; Sharkov, A. V.; Blokhin, A. P.; Tolstorozhev, G. B.

1992-04-01

303

Preconceptual design of the gas-phase decontamination demonstration cart  

Microsoft Academic Search

Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker

Munday

1993-01-01

304

Molecular Tagging Velocimetry (MTV) measurements in gas phase flows  

Microsoft Academic Search

Recent developments in Molecular Tagging Velocimetry (MTV) using the phosphorescence of biacetyl are described for gas-phase flows. With improvements in tagging, detection, and processing\\u000a schemes, whole-field measurements of two components of the velocity vector are obtained simultaneously, typically at more\\u000a than 300 points over a plane. Application of this measurement approach is demonstrated in mapping the velocity and vorticity\\u000a fields

B. Stier; M. M. Koochesfahani

1999-01-01

305

Gas–liquid two-phase flow in microchannels Part I: two-phase flow patterns  

Microsoft Academic Search

Capillary gas–liquid two-phase flow occurs in increasingly more modern industrial applications. The existing relevant data are limited and are inconsistent with respect to the reported flow patterns and their transition boundaries. A systematic experimental investigation of two-phase flow patterns in microchannels was the objective of this study.Using air and water, experiments were conducted in circular microchannels with 1.1 and 1.45mm

K. A. Triplett; S. M. Ghiaasiaan; S. I. Abdel-Khalik; D. L. Sadowski

1999-01-01

306

Multicomponent dynamical nucleation theory and sensitivity analysis.  

PubMed

Vapor to liquid multicomponent nucleation is a dynamical process governed by a delicate interplay between condensation and evaporation. Since the population of the vapor phase is dominated by monomers at reasonable supersaturations, the formation of clusters is governed by monomer association and dissociation reactions. Although there is no intrinsic barrier in the interaction potential along the minimum energy path for the association process, the formation of a cluster is impeded by a free energy barrier. Dynamical nucleation theory provides a framework in which equilibrium evaporation rate constants can be calculated and the corresponding condensation rate constants determined from detailed balance. The nucleation rate can then be obtained by solving the kinetic equations. The rate constants governing the multistep kinetics of multicomponent nucleation including sensitivity analysis and the potential influence of contaminants will be presented and discussed. PMID:15267849

Kathmann, Shawn M; Schenter, Gregory K; Garrett, Bruce C

2004-05-15

307

Contrail formation: Homogeneous nucleation of H2SO4\\/H2O droplets  

Microsoft Academic Search

Homogeneous nucleation of sub-nanometer H2SO4\\/H2O germs, their growth and freezing probability in the cooling wake of a subsonic jet aircraft at tropopause altitude are investigated. Heteromolecular condensation, water uptake, and coagulation cause a small subset of the germs to grow into nm-sized solution droplets which overcome the Kelvin barrier. These droplets efficiently take up water vapor from the gas phase,

B. Kaercher; Th. Peter; R. Ottmann

1995-01-01

308

Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption  

SciTech Connect

A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer is used for the increase of absorption rate, and plays the role of transportation of CO{sub 2}. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the liquid mass transfer coefficients for the CO{sub 2}-water-organic layer system. For the CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system, the enhanced factor is not only dependent on the liquid mass transfer coefficients, but also the chemical reaction rates.

Tim Fout

2007-06-30

309

Gas phase dosimetry connected with radiation processing of industrial flue gas  

NASA Astrophysics Data System (ADS)

The concise review of dosimetric methods suitable for gas phase is presented. The spatial dose distribution from low energy high power electron accelerators, the ELV-3A type, inside the process vessel of industrial flue gases was measured. Complementary measurements using small power and the same energy Van de Graaff were also performed. The agreement between measured and theoretically predicted results is satisfactory.

Panta, P. P.

310

GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN  

EPA Science Inventory

Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

311

The partitioning of Nitric Acid between the gas phase and condensed phase of aqueous sulfate aerosols.  

NASA Astrophysics Data System (ADS)

The heterogeneous hydrolysis of N2O_5 on aqueous aerosol surfaces is an important source of atmospheric HNO3. We generated HNO3 by heterogeneous hydrolysis of N2O_5 on aqueous ammonium and sodium sulfate aerosols and studied its partitioning between the gas phase and the aerosol phase. The experiments were performed in the large aerosol chamber at the FZ-Jülich at several relative humidities. Gas phase processes and the composition of the aerosols were monitored on-line simultaneously by FTIR spectroscopy and by Steam Jet Aerosol Collection/Ion Chromatography. The aerosol size distributions in the range of 20 nm to 5 ? m were measured by differential electromobility classification and by aerodynamic particle sizing. In the presence of aqueous bisulfate and sulfate aerosols a fast heterogeneous formation HNO3 is observed. (The reaction probability of N2O_5 is about 0.02.) In the case of the acidic bisulfate aerosols the major fraction of heterogeneously formed HNO3 resides in the gas phase. For neutral sulfate aerosols a significant fraction of HNO3 is taken up by the condensed phase of the aerosols. This leads to a distinctive growth of the aerosol population during the heterogeneous hydrolysis of N2O_5, which is observable in the number size distribution as well as in IR extinction measurements. The observed partitioning of HNO3 between gas phase and aqueous aerosol phase can be quantitatively understood by a Pitzer based thermodynamic model for salt solutions of high ionic strength. The model calculations and low resolution FTIR spectroscopy demonstrate that protonation of sulfate to bisulfate is the driving force for the uptake of HNO3 in neutral sulfate aerosols.

Mentel, T. F.; Folkers, M.; Sebald, H.; Wahner, A.

2001-12-01

312

Nucleation of Nanoparticle Superclusters from Solution  

NASA Astrophysics Data System (ADS)

Colloids of surface ligated nanoparticles (NP) often act as solutions with the NP displaying reversible temperature and solvent dependent solubility. In many cases when the nanoparticles are highly uniform, the precipitating solid is a two- or three-dimensional superlattice of the nanoparticles. Thus there is strong analogy to the phase behavior of molecular solutions, and it is reasonable to ask what controls the phase behavior of nanoparticle solutions and what is the nature of nucleation and growth of the insoluble phase? We have recently developed [1] a phenomenological model for the effective interaction potential between two ligated gold nanoparticles. In the current work, we carry out Brownian Dynamics simulations using this NP-NP interaction potential. We will report results from our simulations for both dynamics and shape of pre- nucleating and post-nucleating superclusters. [4pt] [1] S.J. Khan, F. Pierce, C.M. Sorensen and A. Chakrabarti, Langmuir, 25, 13861 (2009).

Khan, Siddique J.; Sorensen, C. M.; Chakrabarti, A.

2011-03-01

313

Binary Phase Shaping for Selective Single-Beam CARS Spectroscopy and Imaging of Gas-Phase Molecules (Postprint).  

National Technical Information Service (NTIS)

We report on mode-selective single-beam coherent anti-Stokes Raman spectroscopy (CARS) of gas-phase molecules. Binary phase shaping (BPS) is used to produce single-mode excitation of O2, N2, and CO2 vibrational modes in ambient air and gas phase mixtures,...

B. Xu D. Pestov M. Dantus P. J. Wrzesinski V. V. Lozovoy

2012-01-01

314

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post-processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions. Levitation processing of refractory materials in ultra high vacuum provides an avenue to conduct these kinetic studies on single samples. Two experimental methods have been identified where ultra high vacuum experiments are possible; electrostatic levitation in ground-based experiments and electromagnetic processing in low earth orbit on TEMPUS. Such experiments, reported here, were conducted on zirconium. Liquid zirconium is an excellent solvent and has a high solubility for contaminants contained in the bulk material as well as those contaminants found in the vacuum environment. Oxides, nitrides, and carbides do not exist in the melt, and do not form on the surface of molten zirconium, for the materials and vacuum levels used in this study. Ground-based experiments with electrostatic levitation have shown that the statistical nucleation kinetic experiments are viable and yield results which are consistent with classical nucleation theory. The advantage of low earth orbit experiments is the ability to vary the flow conditions in the liquid prior to nucleation. The put-pose of nucleation experiments in TEMPUS was to examine.

Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

1998-01-01

315

Gas phase self-association of Eudistomin U controlled by gas phase acidity and origin of its interaction with nucleobases  

Microsoft Academic Search

Electrospray ionization mass spectrometry was used to investigate the intrinsic chemical properties of ?-carbolines: Eudistomin U (as EU) and 5-Br-Eudistomin U (as BrEU) yielding self-association in negative ion mode. It was observed that the deprotonated homodimer of EU was more stable in the gas phase than BrEU. Indeed, BrEU presents a higher polarizability that could influence the dimerization energy. On

Ying Xu; Carlos Afonso; Yves Gimbert; Françoise Fournier; Xiaochun Dong; Ren Wen; Jean-Claude Tabet

2009-01-01

316

Modeling of multicomponent homogeneous nucleation using continuous thermodynamics  

Microsoft Academic Search

A theory of homogeneous nucleation in a multicomponent vapor is developed by combining classic nucleation and continuous thermodynamics concepts. The perfect gas equation of state is used in conjunction with this theory to obtain a model valid at low vapor pressures. The theory is applied to kerosenes used for fuels in aeronautics (Jet A, JP-7, and RP-1) at temperatures from

Kenneth Harstad; Josette Bellan

2004-01-01

317

Musculoskeletal-induced Nucleation in Altitude Decompression Sickness  

NASA Technical Reports Server (NTRS)

Musculoskeletal activity has the potential to both improve and compromise decompression safety. Exercise enhances inert gas elimination during oxygen breathing prior to decompression (prebreathe), but it may also promote bubble nuclei formation (nucleation), which can lead to gas phase separation and bubble growth and increase the risk of decompression sickness (DCS). The timing, pattern and intensity of musculoskeletal activity and the level of tissue supersaturation may be critical to the net effect. There are limited data available to evaluate cost-benefit relationships. Understanding the relationship is important to improve our understanding of the underlying mechanisms of nucleation in exercise prebreathe protocols and to quantify risk in gravity and microgravity environments. Data gathered during NASA's Prebreathe Reduction Program (PRP) studies combined oxygen prebreathe and exercise followed by low pressure (4.3 psi; altitude equivalent of 30,300 ft [9,235 m]) microgravity simulation to produce two protocols used by astronauts preparing for extravehicular activity. Both the Phase II/CEVIS (cycle ergometer vibration isolation system) and ISLE (in-suit light exercise) trials eliminated ambulation to more closely simulate the microgravity environment. The CEVIS results (35 male, 10 female) serve as control data for this NASA/Duke study to investigate the influence of ambulation exercise on bubble formation and the subsequent risk of DCS.

Pollock, N. W.; Natoli, M. J.; Conkin, J.; Wessel, J. H., III; Gernhardt, M. L.

2014-01-01

318

A photothermal interferometer for gas-phase ammonia detection.  

PubMed

Detection of gas-phase ammonia is particularly challenging because ambient ammonia concentrations may be less than 1 ppb (molecules of NH(3) per 10(9) molecules of air), ammonia sticks to many materials commonly used to sample air, and particles containing ammonium may interfere with gas-phase measurements. We have built a new and sensitive photothermal interferometer to detect gas-phase ammonia in situ, under typical atmospheric conditions. Ammonia molecules in sampled air absorb infrared radiation from a CO(2) laser at 9.22 ?m, with consequent collisional heating, expansion, and refractive index change. This change in refractive index is detected as a phase shift in one arm of a homodyne interferometer. Measurements of vibrational and electrical noise in the interferometer correlate to an instrumental lower limit of detection of 6.6 ppt ammonia in 1 s. The CO(2) laser output is modulated at 1.2 kHz, and the ac signal from the interferometer is measured with a lock-in amplifier. The detector is zeroed by sampling through a H(3)PO(4)-coated denuder tube and is calibrated by dynamic dilution of two permeation tube outputs and by standard addition. Signal gain is insensitive to CO(2) or H(2)O in the sample, and the signal is linear over 5 orders of magnitude. The instrument 2? precision is 31 ppt when the signal is integrated for 100 s and 250 ppt with a 1-s integration time. The windowless sample cell and inlet is fabricated entirely of glass to minimize sample loss and hysteresis. The instrument response time is demonstrated to be about 1 s. PMID:21662962

Owens, M A; Davis, C C; Dickerson, R R

1999-04-01

319

DSMC Convergence for Microscale Gas-Phase Heat Conduction  

NASA Astrophysics Data System (ADS)

The convergence of Bird's Direct Simulation Monte Carlo (DSMC) method is investigated for gas-phase heat conduction at typical microscale conditions. A hard-sphere gas is confined between two fully accommodating walls of unequal temperature. Simulations are performed for small system and local Knudsen numbers, so continuum flow exists outside the Knudsen layers. The ratio of the DSMC thermal conductivity to the Chapman-Enskog value in the central region is determined for over 200 combinations of time step, cell size, and number of computational molecules per cell. In the limit of vanishing error, this ratio approaches 1.000 to within the correlation uncertainty. In the limit of infinite computational molecules per cell, the difference from unity depends quadratically on time step and cell size as these quantities become small. The coefficients of these quadratic terms are in good agreement with Green-Kubo values found by Hadjiconstantinou, Garcia, and co-workers. These results demonstrate that DSMC can accurately simulate microscale gas-phase heat conduction. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Rader, D. J.; Gallis, M. A.; Torczynski, J. R.

2004-11-01

320

Effect of uniform electric field on homogeneous vapor-liquid nucleation and phase equilibria. II. Extended simple point charge model water  

Microsoft Academic Search

The effects of a uniform electric field on homogeneous vapor-liquid nucleation of the extended simple point charge (SPC\\/E) model water have been simulated. A grand canonical Monte Carlo simulation approach [I. Kusaka et al., J. Chem. Phys. 108, 3416 (1998)], which directly gives the equilibrium distribution of physical clusters, is employed to calculate the formation free energy of the SPC\\/E

G. T. Gao; K. J. Oh; X. C. Zeng

1999-01-01

321

AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)  

EPA Science Inventory

An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

322

Comparative study on methodology in molecular dynamics simulation of nucleation.  

PubMed

Gas-liquid nucleation of 1000 Lennard-Jones atoms is simulated to evaluate temperature regulation methods and methods to obtain nucleation rate. The Berendsen and the Andersen thermostats are compared. The Berendsen thermostat is unable to control the temperature of clusters larger than the critical size. Independent of the thermostating method the velocities of individual atoms and the translational velocities of clusters up to at least six atoms are accurately described by the Maxwell velocity distribution. Simulations with the Andersen thermostat yield about two times higher nucleation rates than those with the Berendsen thermostat. Nucleation rate is extracted from the simulations by direct observation of times of nucleation onset and by the method of Yasuoka and Matsumoto [J. Chem. Phys. 109, 8451 (1998)]. Compared to the direct observation, the nucleation rates obtained from the method of Yasuoka and Matsumoto are higher by a factor of 3. PMID:17581073

Julin, Jan; Napari, Ismo; Vehkamäki, Hanna

2007-06-14

323

Mechanisms of the water-gas-shift reaction by iron pentacarbonyl in the gas phase.  

PubMed

We analyzed the mechanisms of the water-gas-shift reaction catalyzed by Fe(CO) 5/OH (-) in the gas phase using DFT methods. The systematic analysis of the accessible reaction mechanisms and the consideration of the Gibbs free energies allows for different reaction routes than previously suggested. In the dominant catalytic cycle, the hydride [FeH(CO) 4]- is the important intermediate. Associative reaction mechanisms are not favorable under moderate and low pressures. At high pressure, a side reaction takes over and prevents the conversion of H 2O and CO to H 2 and CO 2 and leads to the formation of HCOOH. PMID:18754658

Rozanska, Xavier; Vuilleumier, Rodolphe

2008-10-01

324

Fluorescence Spectroscopy of Gas-phase Polycyclic Aromatic Hydrocarbons  

NASA Astrophysics Data System (ADS)

The purpose of this investigation was to produce fluorescence spectra of polycyclic aromatic hydrocarbon (PAH) molecules in the gas-phase for comparison with blue luminescence (BL) emission observed in astrophysical sources te{ref2,ref3,ref4}. The BL occurs roughly from 350 to 450 nm, with a sharp peak near 380 nm. PAHs with three to four rings, e.g. anthracene and pyrene, were found to produce luminescence in the appropriate spectral region, based on existing studies. Relatively few studies of the gas-phase fluorescence of PAHs exist; those that do exist have dealt primarily with the same samples commonly available for purchase such as pyrene and anthracene. In an attempt to understand the chemistry of the nebular environment we also obtained several nitrogen substituted PAHs from our colleagues at NASA Ames. In order to simulate the astrophysical environment we also took spectra by heating the PAHs in a flame. The flame environment counteracts the formation of eximers and permits the spectroscopy of free-flying neutral molecules. Experiments with coal tar demonstrate that fluorescence spectroscopy reveals primarily the presence of the smallest molecules, which are most abundant and which possess the highest fluorescence efficiencies. One gas-phase PAH that seems to fit the BL spectrum most closely is phenanthridine. In view of the results from the spectroscopy of coal tar, a compound containing a mixture of PAHs ranging from small to very large PAH molecules, we can not preclude the presence of larger PAHs in interstellar sources exhibiting BL.

Thomas, J. D.; Witt, A. N.

325

Gas-phase basicities around and below water revisited.  

PubMed

This work employs Fourier transform ion cyclotron resonance (FT-ICR) and the Gaussian quantum chemistry composite methods W1 and G2 to experimentally and computationally analyze gas-phase basicities (GB) for a series of weak bases in the basicity region around and below water. The study aims to clarify the long-standing discrepancy between reported GB values for weak bases obtained via high-pressure mass spectrometry (HPMS) and ICR; the ICR scale is observed to be more than 2 times contracted compared to the HPMS scale. The computational results of this work support published HPMS data. This agreement improves with increasing sophistication of the computational method and is excellent at the W1 level. Several equilibria were also re-examined experimentally using FT-ICR. In the experiments with some polyfluorinated weak bases (hexafluoro-2-propanol and nonafluoro-2-methyl-2-propanol), it was found that two protonation processes compete in the gas phase: protonation on oxygen and protonation on fluorine. In these species, protonation on fluorine proceeds faster and is statistically favored over protonation on oxygen but leads to cations that are thermodynamically less stable than oxygen-protonated cations. The process may also lead to the irreversible loss of HF. The rearrangement of fluorine-protonated cations to oxygen-protonated cations is very slow and is further suppressed by the process of HF abstraction. These results at least partially explain the discrepancy between published HPMS data and earlier FT-ICR findings and call for the utmost care in using FT-ICR for gas-phase basicity measurements of heavily fluorinated compounds. The narrower dynamic range of ICR necessitates the measurement of several problematic bases and produces some differences between the ICR results in the present work and the published HPMS data; the wider dynamic range allows HPMS to overcome these difficulties in connecting the ladder. PMID:20831239

Leito, Ivo; Koppel, Ilmar A; Burk, Peeter; Tamp, Sven; Kutsar, Martin; Mishima, Masaaki; Abboud, José-Luis M; Davalos, Juan Z; Herrero, Rebeca; Notario, Rafael

2010-10-01

326

Gas Phase Study of C+ Reactions of Interstellar Relevance  

NASA Astrophysics Data System (ADS)

The current uncertainty in many reaction rate constants causes difficulties in providing satisfactory models of interstellar chemistry. Here we present new measurements of the rate constants and product branching ratios for the gas phase reactions of C+ with NH3, CH4, O2, H2O, and C2H2, using the flowing afterglow-selected ion flow tube (FASIFT) technique. Results were obtained using two instruments that were separately calibrated and optimized; in addition, low ionization energies were used to ensure formation of ground-state C+, the purities of the neutral reactants were verified, and mass discrimination was minimized.

Martinez, Oscar, Jr.; Betts, Nicholas B.; Villano, Stephanie M.; Eyet, Nicole; Snow, Theodore P.; Bierbaum, Veronica M.

2008-10-01

327

Laser and Fourier Transform Spectroscopy of Gas Phase Molecules  

Microsoft Academic Search

Laser and Fourier transform spectroscopy were used to study a variety of gas phase molecules. A series of calcium and strontium monoalkoxides, CaOR and SrOR (R=H, CH_3, CH _2CH_3, CH(CH _3)_2, CH_2CH _2CH_3, CH _2(CH_2)_2 CH_3, CH_2 (CH_3)CH_2 CH_3 and C(CH_3) _3) was studied by laser induced fluorescence and laser excitation techniques. The A - X and B - X

Leah Christine O'Brien

1987-01-01

328

Gas–liquid two-phase flow in microchannels  

Microsoft Academic Search

Void fraction and two-phase frictional pressure drop in microchannels were experimentally investigated. Using air and water, experiments were conducted in transparent circular microchannels with 1.1 and 1.45mm inner diameters and in microchannels with semi-triangular (triangular with one corner smoothed) cross-sections with hydraulic diameters 1.09 and 1.49mm. Gas and liquid superficial velocities were varied in the 0.02–80m\\/s and 0.02–8m\\/s ranges, respectively,

K. A. Triplett; S. M. Ghiaasiaan; S. I. Abdel-Khalik; A. LeMouel; B. N. McCord

1999-01-01

329

Neurotransmitters in the Gas Phase: La-Mb Studies  

NASA Astrophysics Data System (ADS)

LA-MB-FTMW spectroscopy combines laser ablation with Fourier transform microwave spectroscopy in supersonic jets overcoming the problems of thermal decomposition associated with conventional heating methods. We present here the results on LA-MB-FTMW studies of some neurotransmitters. Six conformers of dopamine, four of adrenaline, five of noradrenaline and three conformers of serotonin have been characterized in the gas phase. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of different conformers and the experimental characterization of the intramolecular forces at play which control conformational preferences.

Cabezas, C.; Mata, S.; López, J. C.; Alonso, J. L.

2011-06-01

330

Raman study of vibrational dynamics of aminopropylsilanetriol in gas phase  

NASA Astrophysics Data System (ADS)

Raman spectrum of aminopropylsilanetriol (APST) in gas phase has been recorded at room temperature in macro chamber utilizing two-mirror technique over the sample tube. Unlike predominantly trans molecular conformation in condensed phase, the spectra of vapor show that the molecules are solely in gauche conformation with intramolecular hydrogen bond N⋯Hsbnd O which reduces the molecular energy in respect to trans conformation by 0.152 eV. The assignment of the molecular spectra based on the DFT calculation is presented. The strong vibrational bands at 354 cm-1, 588 cm-1 and 3022 cm-1 are proposed for verifying the existence of the ring like, hydrogen bonded structure. Special attention was devoted to the high frequency region, where hydrogen bond vibrations are coupled to stretchings of amino and silanol groups.

Volovšek, V.; Danani?, V.; Bistri?i?, L.; Movre Šapi?, I.; Furi?, K.

2014-01-01

331

Energy effects in bubble nucleation  

SciTech Connect

Bubble size and number produced by desorption are important considerations for certain industrial processes such as flotation, gas stripping, and some types of chemical reactions and mass transfer. The size and number of bubbles produced by the desorption of supersaturated gases from water are shown to be a primary function of the energy available for bubble formation in a flowing system; this energy is that not dissipated in turbulence and friction. The number of nucleation sites is greatly increased when certain impurities are present, particularly surface-active agents. Low saturation pressures can produce very large numbers of very small bubbles when added energy is provided for discharge. High gas concentrations produce excess large bubbles which pass up rapidly through the much slower rising bubble mass. A combination of low saturation pressure followed by higher pressure for flow, such as by liquid pumping, results in bubble characteristics which can be controlled for applications.

Jackson, M.L. (Univ. of Idaho, Moscow, ID (United States). Dept. of Chemical Engineering)

1994-04-01

332

Bubble nucleation in lipid bilayers: a mechanism for low frequency ultrasound disruption.  

PubMed

Recent experiments have shown that low frequency ultrasound (LFUS) induces leakage from lipid vesicles. However, the mechanism by which LFUS disrupts the lipid bilayer structure is not clear. In this paper we develop a theoretical model to test the possibility that gas molecule partitioning from the aqueous media into the lipid bilayer core can lead to the nucleation of microscale gas bubbles. If those can, indeed, form, then their presence in the lipid bilayer and interactions with an ultrasound field can cause bilayer disruption and leakage. The model derived here for the nucleation of stable bubbles accounts for the 'surface tension' that the lipid bilayer exerts on the bubble, a result of the associated disruption of the lipid packing. The model predicts that the probability of bubble nucleation is highly sensitive to the bilayer thickness, and largely insensitive to the bilayer phase. The probability of stable bubble formation is shown to correlate with experimentally measured sensitivity of lipid bilayers to LFUS, suggesting that membrane disruption may be due to embedded bubbles that nucleated in the bilayer. PMID:23313452

Wrenn, Steven P; Small, Eleanor; Dan, Nily

2013-04-01

333

Experimental study of Gas Phase Formation and Evolution in Low fO2 Planetary Basalts.  

NASA Astrophysics Data System (ADS)

The existence of a gas phase in planetary basaltic magmas is demonstrated by the ubiquitous presence of vesicles in returned lunar samples and meteorites as well as basalts from Earth and Mars. Additionally, formation of the fine-grained glass bead deposits during eruption of lunar picritic glasses required a large gas-bubble volume (> 90%) at the time of eruption/fragmentation. Up to 100-200 ppm levels of H, S, Cl and F still remain as diffusion-loss profiles in individual lunar glass beads SIMS (1), and higher volatile concentrations occur in olivine melt inclusions (2). The composition and origin of such volcanic gases were investigated by experiments on a volatile (C-O-H-S-Cl-F)-bearing picritic glass composition as a function of fO2 near iron-wustite (IW). The C-O-H species dissolved in gas-saturated basaltic melt above IW-0.5 are carbonate, OH and H2O with 100 to 10,000 ppm H2O in the sample; below IW-0.5, the C-species present (Raman and FTIR) are Fe(CO)5 (iron pentacarbonyl) and lesser CH4 [3]. The change in melt speciation in part reflects a change in calculated speciation in the coexisting gas [4]. The carbon solubility in these experimental melts increases linearly with increasing pressure; the more oxidized glasses contain 32-620 ppm C for pressures of 98 to 980 MPa, the reduced glasses contain 8-240 ppm C for pressures between 36 and 900 MPa. Thus, the C solubility of the more reduced Fe-carbonyl and CH4 is about one-half that of carbonate at the same pressure, and indicates the carrying capacity for C in reduced (i.e., lunar) magmas is much lower than it is in present day terrestrial magmas. Varioles up to 200 um in diameter formed in some experiments with higher dissolved water contents (1%); they have radiating crystalline textures (olivine, glass and poorly crystallized graphite) initiated at a central nucleation site. A sharp peak in the variole Ramen spectra indicates methane as well as CO is released during variole formation and a reaction such as 2CO = C +CO2 formed the graphite. Several series of experiments on chips of low fO2 glass created at high pressure quantify S, Cl and F partitioning into the H2O-CO gas phase with decompression steps from 200 to 40 MPa. A gas formed with the first pressure drop, indicating melt supersaturation with CO and/or CH4; H2O and lesser amounts of S, Cl and F partitioned into the initial gas, and continued to do so with additional drops in pressure. The ubiquitous Fe-metal seen in lunar picritic glasses may form by graphite oxidation, but also may form by breakdown of Fe(CO)5 as the melt continues to saturate during ascent. [1] A. E. Saal et al.(2008) Nature 454, 192-195. [2] E. H. Hauri et al (2011) Science 333, 213 -215. [3] Wetzel, D., Rutherford, M.J. Jacobsen S.D., Hauri, E.H., and Saal, A.E., (submitted); Nature Geoscience Aug. 1, 2012. [4] Zhang, C. and Duan, Z. (2009) GCA, 73, 2089-2102.

Rutherford, M. J.; Wetzel, D. T.; Saal, A. E.; Hauri, E. H.

2012-12-01

334

Nucleation and crystallization in calcium aluminate glasses  

Microsoft Academic Search

The crystallization and nucleation mechanisms of a eutectic composition (46.5 wt% CaO, 53.5 wt% Al2O3) calcium aluminate glass were investigated by DTA, XRD and SEM. The crystallization temperature was found to vary from 940°C to 1040°C, and two phases appeared in the crystallized samples: Ca12Al14O33 (major phase) and CaAl2O4 (minor phase). Two kinds of crystal structures, dendritic and spherulitic, were

Wenyan Li; Brian S. Mitchell

1999-01-01

335

Surface-Specific Nucleation and Deposition (?) of Heavy and Precious Metals on Minerals and Fibers Exposed to Fumarole Gas - FESEM/EDS Studies  

NASA Astrophysics Data System (ADS)

Mineral grains, glass fibers and diatoms had been exposed to the F0 fumarole at Vulcano (Italy) between 2001 and 2004. On quartz grains patches of Pb-(Tl)-Cl (max.l=50 µm), Tl-(Fe)-(Br)-Cl, Al-S-Cl-(O), Al-Cl-(F)-(S)-(Mg)-(K)-(Ca)-(Fe) and needle-like Ca sulphate (+Cl-F) are growing. Pb-S nucleated on K feldspar, Ba-S-O and As-S on the surface of diatoms. Desert dust interacting with volcanic gases might transport heavy metals to environments far away from volcanoes. Si-rich glass fibers are the substratum for Tl-Cl, Hg-, As-, Tl- and Pb-bearing and Al-(S)-(O) crystals. Au-Ag alloys (l= ca. 3 µm) are detected on Si-rich fibers. These anhedral grains are embedded in an Al-O-(S)-(Ca) matrix. Available data do not indicate if deposition or nucleation are the responsible processes. Ba-S-O particles nucleated on borosilicate glass fibers. Rock wool of basaltic composition (Na-Mg-Al-Si-K-Ca-Ti-Fe-O) collected only S and shows surface modification. These preliminary results indicate that Si-rich surfaces might be useful in i.e. air conditioning systems to detoxicate volcanically polluted air. Quartz sand deployed on top of lava flows might reduce the release of heavy metals to the environment. According to the experiments utilizing glass fibers of different composition the eruptions of basaltic magma should release more heavy metals to the atmosphere relatively compared to the eruptions of rhyolitic magma.

Obenholzner, J. H.; Poelt, P.; Reichmann, A.

2004-12-01

336

Surface-Specific Nucleation and Deposition (?) of Heavy and Precious Metals on Minerals and Fibers Exposed to Fumarole Gas - FESEM\\/EDS Studies  

Microsoft Academic Search

Mineral grains, glass fibers and diatoms had been exposed to the F0 fumarole at Vulcano (Italy) between 2001 and 2004. On quartz grains patches of Pb-(Tl)-Cl (max.l=50 µm), Tl-(Fe)-(Br)-Cl, Al-S-Cl-(O), Al-Cl-(F)-(S)-(Mg)-(K)-(Ca)-(Fe) and needle-like Ca sulphate (+Cl-F) are growing. Pb-S nucleated on K feldspar, Ba-S-O and As-S on the surface of diatoms. Desert dust interacting with volcanic gases might transport heavy

J. H. Obenholzner; P. Poelt; A. Reichmann

2004-01-01

337

Nucleation of protein fibrillation by nanoparticles  

PubMed Central

Nanoparticles present enormous surface areas and are found to enhance the rate of protein fibrillation by decreasing the lag time for nucleation. Protein fibrillation is involved in many human diseases, including Alzheimer's, Creutzfeld-Jacob disease, and dialysis-related amyloidosis. Fibril formation occurs by nucleation-dependent kinetics, wherein formation of a critical nucleus is the key rate-determining step, after which fibrillation proceeds rapidly. We show that nanoparticles (copolymer particles, cerium oxide particles, quantum dots, and carbon nanotubes) enhance the probability of appearance of a critical nucleus for nucleation of protein fibrils from human ?2-microglobulin. The observed shorter lag (nucleation) phase depends on the amount and nature of particle surface. There is an exchange of protein between solution and nanoparticle surface, and ?2-microglobulin forms multiple layers on the particle surface, providing a locally increased protein concentration promoting oligomer formation. This and the shortened lag phase suggest a mechanism involving surface-assisted nucleation that may increase the risk for toxic cluster and amyloid formation. It also opens the door to new routes for the controlled self-assembly of proteins and peptides into novel nanomaterials.

Linse, Sara; Cabaleiro-Lago, Celia; Xue, Wei-Feng; Lynch, Iseult; Lindman, Stina; Thulin, Eva; Radford, Sheena E.; Dawson, Kenneth A.

2007-01-01

338

Nucleation and growth of chemical vapor deposited diamond films  

Microsoft Academic Search

This research involves a study of the nucleation and growth processes during diamond chemical vapor deposition (CVD) via numerical modeling and simulations. Numerical models have been developed: (1) to examine the chemistry of the intermediate layer that forms at the interface between diamond and non-diamond substrate, (2) to understand the nucleation, size and structure of diamond phase carbon clusters on

Pushpa Mahalingam

1997-01-01

339

A universal tool to investigate nucleation from aqueous solutions  

NASA Astrophysics Data System (ADS)

It has turned out that on-line monitoring of conductivity and turbidity is a universal tool to study nucleation from aqueous solutions. In this paper, we describe an experimental setup allowing to determine the onset of nucleation from aqueous phases. Examples are presented for emulsion polymerization of different monomers and precipitation reactions of different salts. .

Tauer, Klaus; Padtberg, Klaus

2000-08-01

340

Heterogeneous nucleation during solidification of undercooled alloy droplets  

Microsoft Academic Search

The Droplet Emulsion Technique was used for the synthesis of Bi-Cd droplet samples. Thermal cycles provided a conditioning treatment that resulted in a stable nucleation exotherm and droplet microstructure. The primary Bi phase in hypoeutectic droplets was confirmed as the operative nucleant for the nucleation of Cd from the liquid at a substantial amount of undercooling. The analysis of isothermal

Peter Georg Hoeckel

1999-01-01

341

Gas phase self-association of Eudistomin U controlled by gas phase acidity and origin of its interaction with nucleobases  

NASA Astrophysics Data System (ADS)

Electrospray ionization mass spectrometry was used to investigate the intrinsic chemical properties of [beta]-carbolines: Eudistomin U (as EU) and 5-Br-Eudistomin U (as BrEU) yielding self-association in negative ion mode. It was observed that the deprotonated homodimer of EU was more stable in the gas phase than BrEU. Indeed, BrEU presents a higher polarizability that could influence the dimerization energy. On the contrary, the stability energies calculated at B3LYP/6-31+G*//AM1 level showed a small difference for these two dimers. To understand the experimental stability variation, the experimental and theoretical gas phase acidities of these two [beta]-carbolines have been estimated. It has been shown that EU is less acidic than BrEU in the gas phase, which could explain the lower stability of the [2BrEU-H]- dimer. In addition, the investigation of non-covalent interaction of [beta]-carbolines and nucleobases has been carried out. It was experimentally demonstrated that the deprotonated heterodimer's relative stability scale was [Gua + M-H]- >> [Thy + M-H]- > [Ade + M-H]-, but the Cyt/[beta]-carboline complexes were not observed. However, the absence of Cyt/[beta]-carboline complexes could be explained by the great acidity difference between Cyt and [beta]-carbolines, yielding unstable non-covalent complexes. The studied [beta]-carbolines showed a particular affinity with guanine which suggested a strong interaction, from a structural and reactivity point of view. Calculated reaction pathways rationalize the set of experimental results concerning the heterodimer stabilisation reflected by the V1/2 value of breakdown curves of deprotonated heterodimers.

Xu, Ying; Afonso, Carlos; Gimbert, Yves; Fournier, Françoise; Dong, Xiaochun; Wen, Ren; Tabet, Jean-Claude

2009-09-01

342

Gas-Phase Fragmentation Analysis of Nitro-Fatty Acids  

NASA Astrophysics Data System (ADS)

Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO{2/-} anion or neutral loss of HNO2. The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional ? or ? unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond ? electrons during NO{2/-} rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of 13C and 15N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples.

Bonacci, Gustavo; Asciutto, Eliana K.; Woodcock, Steven R.; Salvatore, Sonia R.; Freeman, Bruce A.; Schopfer, Francisco J.

2011-09-01

343

Gas phase absorption studies of photoactive yellow protein chromophore derivatives.  

PubMed

Photoabsorption spectra of deprotonated trans p-coumaric acid and two of its methyl substituted derivatives have been studied in gas phase both experimentally and theoretically. We have focused on the spectroscopic effect of the location of the two possible deprotonation sites on the trans p-coumaric acid which originate to either a phenoxide or a carboxylate. Surprisingly, the three chromophores were found to have the same absorption maximum at 430 nm, in spite of having different deprotonation positions. However, the absorption of the chromophore in polar solution is substantially different for the distinct deprotonation locations. We also report on the time scales and pathways of relaxation after photoexcitation for the three photoactive yellow protein chromophore derivatives. As a result of these experiments, we could detect the phenoxide isomer within the deprotonated trans p-coumaric acid in gas phase; however, the occurrence of the carboxylate is uncertain. Several computational methods were used simultaneously to provide insights and assistance in the interpretation of our experimental results. The calculated excitation energies S(0)-S(1) are in good agreement with experiment for those systems having a negative charge on a phenoxide moiety. Although our augmented multiconfigurational quasidegenerate perturbation theory calculations agree with experiment in the description of the absorption spectrum of anions with a carboxylate functional group, there are some puzzling disagreements between experiment and some calculational methods in the description of these systems. PMID:19642665

Rocha-Rinza, Toms; Christiansen, Ove; Rajput, Jyoti; Gopalan, Aravind; Rahbek, Dennis B; Andersen, Lars H; Bochenkova, Anastasia V; Granovsky, Alexander A; Bravaya, Ksenia B; Nemukhin, Alexander V; Christiansen, Kasper Lincke; Nielsen, Mogens Brøndsted

2009-08-27

344

Spatial point pattern analysis applied to bubble nucleation in silicate melts  

Microsoft Academic Search

Experimental bubble nucleation studies are used for determining the nucleation mechanism as a function of experimental conditions, the resulting bubble number density, and can also yield estimates of the melt-vapor surface tension. This provides important information on gas exsolution in silicate melts, which can be applied towards understanding magmatic degassing in volcanic conduits. At present, determination of nucleation processes in

Joanna Mongrain; Jessica F. Larsen

2009-01-01

345

Development and application of a new air pollution modeling system-part I: Gas-phase simulations  

NASA Astrophysics Data System (ADS)

A new air pollution modeling system is discussed and applied. The system consists of GATOR, a gas, aerosol, transport, and radiation air quality model and MMTD, a mesoscale meteorological and tracer dispersion model. The gas-phase processes treated by GATOR include photochemistry, deposition, emissions, and gas-to-particle conversion. To solve stiff chemical rate equations, a sparse-matrix, vectorized Gear-type code (SMVGEAR) was used. The aerosol processes in GATOR include coagulation, aqueous chemistry, chemical equilibrium, condensational growth, dissolutional growth, evaporation, nucleation, emissions, deposition, and sedimentation. The transport processes include horizontal advection and diffusion and vertical convection and diffusion. Finally, the radiation algorithm calculates ultraviolet, visible, and infrared optical depths, mean intensities for photodissociation rates, and radiative heat fluxes for temperature calculations. The MMTD predicts winds, diffusion, temperature, pressure, humidity, soil moisture, and rainfall. These variables are fed to GATOR and radiative heating rates from GATOR are fed back to the MMTD. With the GATOR/MMTD system, gas-phase pollution was simulated for the Southern California Air Quality Study (SCAQ) days of 26-28 August 1987. Results were compared to surface measurements for many parameters. The model predicted normalized gross errors for ozone of 17.6% and 23.4% at 2:30 p.m. on the first and second days of simulation, respectively. Also, the normalized gross error during the first 12 h of simulation was 22%. Correct emissions and initial mixing ratios appear to be necessary for obtaining good results. Initial conditions outside the basin seem to affect results by the second and third days. Time-series plots, statistics, and a sensitivity test are discussed. Aerosol simulation results will be shown in a later work.

Jacobson, Mark Z.; Lu, Rong; Turco, Richard P.; Toon, Owen B.

346

Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: ab initio simulations supporting center nucleation.  

PubMed

High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 ?m/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10(-9) m(2)/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase. PMID:24852556

André, Yamina; Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Cadiz, Fabian; Rowe, Alistair; Paget, Daniel; Petit, Elodie; Leroux, Christine; Trassoudaine, Agnès; Ramdani, M Réda; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne

2014-05-21

347

Feasibility of gas-phase decontamination of gaseous diffusion equipment  

SciTech Connect

The five buildings at the K-25 Site formerly involved in the gaseous diffusion process contain 5000 gaseous diffusion stages as well as support facilities that are internally contaminated with uranium deposits. The gaseous diffusion facilities located at the Portsmouth Gaseous Diffusion Plant and the Paducah Gaseous Diffusion Plant also contain similar equipment and will eventually close. The decontamination of these facilities will require the most cost-effective technology consistent with the criticality, health physics, industrial hygiene, and environmental concerns; the technology must keep exposures to hazardous substances to levels as low as reasonably achievable (ALARA). This report documents recent laboratory experiments that were conducted to determine the feasibility of gas-phase decontamination of the internal surfaces of the gaseous diffusion equipment that is contaminated with uranium deposits. A gaseous fluorinating agent is used to fluorinate the solid uranium deposits to gaseous uranium hexafluoride (UF{sub 6}), which can be recovered by chemical trapping or freezing. The lab results regarding the feasibility of the gas-phase process are encouraging. These results especially showed promise for a novel decontamination approach called the long-term, low-temperature (LTLT) process. In the LTLT process: The equipment is rendered leak tight, evacuated, leak tested, and pretreated, charged with chlorine trifluoride (ClF{sub 3}) to subatmospheric pressure, left for an extended period, possibly > 4 months, while processing other items. Then the UF{sub 6} and other gases are evacuated. The UF{sub 6} is recovered by chemical trapping. The lab results demonstrated that ClF{sub 3} gas at subatmospheric pressure and at {approx} 75{degree}F is capable of volatilizing heavy deposits of uranyl fluoride from copper metal surfaces sufficiently that the remaining radioactive emissions are below limits.

Munday, E.B.; Simmons, D.W.

1993-02-01

348

Surfactants from the gas phase may promote cloud droplet formation.  

PubMed

Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8-10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas-aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

Sareen, Neha; Schwier, Allison N; Lathem, Terry L; Nenes, Athanasios; McNeill, V Faye

2013-02-19

349

Temperature dependence of nucleation in Yukawa fluids  

NASA Astrophysics Data System (ADS)

We have studied the temperature dependence of gas-liquid nucleation in Yukawa fluids with gradient theory (GT) and density functional theory (DFT). Each of these nonclassical theories exhibits a weaker (i.e. better) temperature dependence than classical nucleation theory. At a given temperature, the difference between GT and DFT for the reversible work to form a critical nucleus gets smaller with increasing superaturation. For the temperature dependence, the reversible work for GT is very close to that for DFT at high temperatures. The difference between the two theories increases with decreasing temperature and supersaturation. Thus, in contrast to the behavior of a Peng-Robinson fluid, we find that GT can improve the temperature dependence over that of classical nucleation theory, although not always to the same degree as DFT.

Li, J.-S.; Wilemski, G.

2002-03-01

350

Atomistic level description of phase diagram of gas clathrate hydrates with complex gas compositions  

NASA Astrophysics Data System (ADS)

An approach has been realized that allows us to construct a p-T phase diagrams of various gas hydrates, three-dimensional hydrogen-bonded water structures in which water molecules arrange themselves in a cage-like (host) structure around gas (guest) molecules, with complex gas compositions [1-2]. In order to evaluate the parameters of weak interactions, a TDDFT formalism and LDA technique entirely in real space have been implemented for calculations of vdW dispersion coefficients for atoms within the all-electron mixed-basis approach. The combination of both methods enables one to calculate thermodynamic properties of clathrate hydrates without resorting to any empirical parameter fittings. Using the proposed method it is possible not only confirm the existing experimental data but also predict the unknown region of thermodynamic stability of clathrate hydrates, and also propose the gas storage ability as well as the gas composition for which high-stability region of clathrate hydrates can be achieved. The proposed method is quite general and can be applied to the various non-stoichiometric inclusion compounds with weak guest-host interactions.[4pt] [1] R. V. Belosludov et al. J. Chem Phys. 131 (2009) 244510[0pt] [2] R. V. Belosludov et al. Mol. Simul. 38 (2012) 773.

Belosludov, R.; Mizuseki, H.; Kawazoe, Y.; Subbotin, O.; Belosludov, V.

2013-03-01

351

Colloids and Nucleation  

NASA Technical Reports Server (NTRS)

The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range (0.505 to 0.575) and compared to classical nucleation rate calculations. The experimental nucleation rate density varies with volume fraction more slowly than expected theoretically. Gravity may influence nucleation because crystal nuclei are more dense than the surrounding fluid and may be gravitationally convected. The largest observed crystal size was near volume fraction 0.52. Near the freezing point, crystals should grow to large size because nuclei are sparse and there is plenty of room to grow without contacting other crystals. Near melting the opposite is true, with crystals growing into one another shortly after nucleation. The maximum crystal size seen near 0.52 volume fraction suggests that gravitational stresses are limiting crystal growth near freezing.

Ackerson, Bruce

1997-01-01

352

Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters  

PubMed Central

Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7–19 monomer units and 2–5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation.

Jurchen, John C.; Garcia, David E.; Williams, Evan R.

2005-01-01

353

Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed  

NASA Astrophysics Data System (ADS)

Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

2010-07-01

354

Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed  

NASA Astrophysics Data System (ADS)

Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

2009-12-01

355

Nucleation of antikaon condensed matter in protoneutron stars  

NASA Astrophysics Data System (ADS)

A first order phase transition from nuclear matter to antikaon condensed matter may proceed through thermal nucleation of a critical droplet of antikaon condensed matter during the early evolution of protoneutron stars (PNS). Droplets of new phase having radii larger than a critical radius would survive and grow, if the latent heat is transported from the droplet surface to the metastable phase. We investigate the effect of shear viscosity on the thermal nucleation time of the droplets of antikaon condensed matter. In this connection we particularly study the contribution of neutrinos in the shear viscosity and nucleation in PNS.

Banik, Sarmistha; Nandi, Rana

2012-04-01

356

Homogeneous nucleation of methane hydrates: unrealistic under realistic conditions.  

PubMed

Methane hydrates are ice-like inclusion compounds with importance to the oil and natural gas industry, global climate change, and gas transportation and storage. The molecular mechanism by which these compounds form under conditions relevant to industry and nature remains mysterious. To understand the mechanism of methane hydrate nucleation from supersaturated aqueous solutions, we performed simulations at controlled and realistic supersaturation. We found that critical nuclei are extremely large and that homogeneous nucleation rates are extremely low. Our findings suggest that nucleation of methane hydrates under these realistic conditions cannot occur by a homogeneous mechanism. PMID:23148735

Knott, Brandon C; Molinero, Valeria; Doherty, Michael F; Peters, Baron

2012-12-01

357

Cooperative effect in nucleation: Nanosized seed particles jointly nucleate vapor-liquid transitions  

NASA Astrophysics Data System (ADS)

Using the constrained lattice density functional theory, in this work we show that when the size of critical nucleus for vapor-liquid transition is comparable to the distance between seed particles (or active sites on solid surfaces), a cooperative effect in nucleation processes is found. More specifically, neighboring seed particles are found to nucleate jointly the phase transition with a lower nucleation barrier and a different morphology of critical nucleus compared to those from an isolated seed particle. In addition, the cooperative effect, including the decrease of nucleation barrier and the morphology change of critical nucleus, is found to depend on the distance between seed particles, the fluid-solid interaction, and the particle size.

Guo, Qiumin; Liu, Yawei; Jiang, Guangfeng; Zhang, Xianren

2013-06-01

358

Cavitation nucleation agents for nonthermal ultrasound therapy.  

PubMed

The use of a nucleation-promoting agent can greatly enhance therapeutically useful nonthermal bioeffects. A blank agent (saline), Optison ultrasound contrast agent, a stabilized perfluoropentane droplet suspension (SDS), and retained air space were compared as nucleation agents in whole blood. Fresh canine whole blood with added agent was exposed in 1.3-ml disposable pipette bulbs to lithotripter shock waves (2-Hz rate; +24.4, -5.2 MPa peak pressure amplitudes). Cavitation activity was assessed by measuring hemolysis. The droplet suspension performed nearly as well as retained air when added at a concentration sufficient to provide a roughly equal volume of gas after vaporization. Optison also yielded nucleation, but a concentration of 10%-20% was needed for large enhancement of hemolysis comparable to 5% SDS. Exposure at room temperature, which was less than the 29 degrees C boiling point of perfluoropentane, eliminated the enhancement of the hemolysis effect relative to the blank. Application of 100-kPa excess pressure during exposure reduced but did not eliminate the nucleation ability of Optison, SDS, or retained air. However, this small pressure (relative to the peak positive pressure of the shock waves) eliminated the hemolysis induced with the blank agent. The stabilized perfluoropentane droplet suspension appears to be a good nucleation agent for nonthermal ultrasound therapy applications. PMID:10875392

Miller, D L; Kripfgans, O D; Fowlkes, J B; Carson, P L

2000-06-01

359

Photofragment fluorescence as a sensitive probe for gas-phase alkali compounds and their photochemistry  

Microsoft Academic Search

Sensitive techniques are needed for the detection of highly corrosive gas-phase alkali compounds in coal gasifier gas turbine streams. We report on the use of photofragment fluorescence as a very sensitive, selective probe for alkali compounds. Photodissociation of a gas-phase alkali compound using a laser at suitably short ultraviolet (uv) wavelengths produces an electronically excited alkali atom. Detection of fluorescence

R. C. Oldenborg; S. L. Baughcum; D. Hof; K. E. Winn

1985-01-01

360

Determination of gas phase adsorption isotherms—a simple constant volume method  

Microsoft Academic Search

Single and ternary solute gas phase adsorption isotherms were conducted in this study to evaluate the effectiveness of a simple constant volume method, which was utilized by using Tedlar gas sampling bags as a constant volume batch reactor. For this purpose, gas phase adsorption of toluene, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) on two types of activated

Daekeun Kim; Zhangli Cai; George A. Sorial

2006-01-01

361

Pressure drop, heat transfer, critical heat flux, and flow stability of two-phase flow boiling of water and ethylene glycol/water mixtures - final report for project "Efficent cooling in engines with nucleate boiling."  

SciTech Connect

Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and to eliminate potential hot spots in engines. However, the fundamental understanding of flow boiling mechanisms of a 50/50 ethylene glycol/water mixture under engineering application conditions is still limited. In addition, it is impractical to precisely maintain the volume concentration ratio of the ethylene glycol/water mixture coolant at 50/50. Therefore, any investigation into engine coolant characteristics should include a range of volume concentration ratios around the nominal 50/50 mark. In this study, the forced convective boiling heat transfer of distilled water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm-inner-diameter circular tube has been investigated in both the horizontal flow and the vertical flow. The two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux of the test fluids were determined experimentally over a range of the mass flux, the vapor mass quality, and the inlet subcooling through a new boiling data reduction procedure that allowed the analytical calculation of the fluid boiling temperatures along the experimental test section by applying the ideal mixture assumption and the equilibrium assumption along with Raoult's law. Based on the experimental data, predictive methods for the two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux under engine application conditions were developed. The results summarized in this final project report provide the necessary information for designing and implementing nucleate-boiling vehicular cooling systems.

Yu, W.; France, D. M.; Routbort, J. L. (Energy Systems)

2011-01-19

362

Gas-phase reactions of halogen species of atmospheric importance  

NASA Astrophysics Data System (ADS)

A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm/molecule/s. The reaction between I and NO3 was found to occur at a rate of about 60 percent of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO3 was found to be (4.5 +/- 1.9) x 10(exp -10)/cu cm/molecule/s. An upper limit for the heat of formation of IONO2 of (21 +/- 3) kJmol(exp -1) was also derived.

Heard, Anne C.

363

Microporous hydrophobic hollow fiber modules for gas-liquid phase separation in microgravity  

Microsoft Academic Search

Gas-liquid interphase mass transfer operations, such as gas-liquid phase separation, gas absorption into liquid or dissolved gas separation from liquid, gas humidification and drying via liquid contact, and evaporative cooling are readily accomplished on the Earth with settling\\/spray chambers, packed towers, or bubble columns. This paper reports on gas-water mass transfer tests performed utilizing microporous hydrophobic Hollow Fiber Modules (HFMs)

Gary Noyes

1993-01-01

364

Nucleating actin for invasion  

Microsoft Academic Search

The invasion of cancer cells into the surrounding tissue is a prerequisite and initial step in metastasis, which is the leading cause of death from cancer. Invasive cell migration requires the formation of various structures, such as invadopodia and pseudopodia, which require actin assembly that is regulated by specialized actin nucleation factors. There is a large variety of different actin

Alexander Nürnberg; Thomas Kitzing; Robert Grosse

2011-01-01

365

Colloids and Nucleation.  

National Technical Information Service (NTIS)

The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studie...

B. Ackerson

1997-01-01

366

Simple correction to the classical theory of homogeneous nucleation.  

PubMed

Formation of the new disperse phase via homogeneous nucleation plays a fundamental role wherever the first-order phase transitions occur. Inconsistent temperature dependence of the nucleation rates and poor agreement of theoretical critical supersaturations with experimental data for a number of substances are fundamental problems of the classical nucleation theory (CNT). Here we show that these problems can be solved with a simple empirical correction to CNT. Despite its simplicity, the corrected CNT (CCNT) accurately predicts temperature dependences and absolute values of the critical supersaturations for both organic and inorganic substances with widely varying properties at different ambient conditions and it works surprisingly well in a wide size range down to few molecules. The difference in predictions of CCNT and other versions of the classical nucleation theory commonly used in analyzing experimental data is discussed. It has been found that CCNT consistently gives better agreement with experimental data than other versions of classical nucleation theory. PMID:15836336

Nadykto, Alexey B; Yu, Fangqun

2005-03-01

367

Nonlinear Acoustical Assessment of Precipitate Nucleation  

NASA Technical Reports Server (NTRS)

The purpose of the present work is to show that measurements of the acoustic nonlinearity parameter in heat treatable alloys as a function of heat treatment time can provide quantitative information about the kinetics of precipitate nucleation and growth in such alloys. Generally, information on the kinetics of phase transformations is obtained from time-sequenced electron microscopical examination and differential scanning microcalorimetry. The present nonlinear acoustical assessment of precipitation kinetics is based on the development of a multiparameter analytical model of the effects on the nonlinearity parameter of precipitate nucleation and growth in the alloy system. A nonlinear curve fit of the model equation to the experimental data is then used to extract the kinetic parameters related to the nucleation and growth of the targeted precipitate. The analytical model and curve fit is applied to the assessment of S' precipitation in aluminum alloy 2024 during artificial aging from the T4 to the T6 temper.

Cantrell, John H.; Yost, William T.

2004-01-01

368

Modeling Aerosol Nucleation  

NASA Technical Reports Server (NTRS)

The goal of this work has been to understand how nitric acid condenses on cirrus ice cloud particles by analyzing data obtained during the SAGE III Ozone Loss and Validation Experiment (SOLVE) research mission based out of Kiruna, Sweden. Ms. Gamblin simultaneously analyzed gas phase nitric acid data along with particulate NO, data, particulate, vapor and gas-phase water data from several different instruments, particle size data, which included surface area and volume measurements, ozone concentration data as well as temperature, pressure and GPS coordinates of the sampled air parcel. All parameters where held constant with only one allowed to vary in order to determine what controls the extent to which nitric acid will condensation on ice. In addition, this data was compared to theoretical values of nitric acid condensation on ice based upon recent laboratory data. Comparison of these two data sets shows the field data does not agree with what is expected in the laboratory at comparable temperatures and nitric acid pressures. The most significant difference is that surface coverages in the atmosphere were found to be elevated relative to surface coverages measured in the laboratory. The results of this study were accepted for publication by Geophysical Research Letters.

Toon, Owen B.; Klein, Kari; Gamblin, Brandy

2003-01-01

369

Microscopic phase-dependent residual stresses in the machined surface layer of two-phase alloy  

Microsoft Academic Search

Residual stresses in the machined surface layer, which affect fatigue crack nucleation and stress corrosion cracking especially in aerospace engines and gas turbines for power generation, depend on microstructures in case of machining a multiple-phase alloy. Hence, the microscopic phase-dependent residual stresses should be known when a machined part is used under critical stress conditions and circumstances. In the present

T. Obikawa; Y. Takemura; Y. Akiyama; J. Shinozuka; H. Sasahara

2009-01-01

370

The intrinsic (gas-phase) acidities of bridgehead alcohols  

NASA Astrophysics Data System (ADS)

The gas-phase acidities of 1-adamantanol and perfluoro1-adamantanol were determined by means of Fourier transform ion cyclotron resonance spectrometry (FT-ICR). The acidity of perfluoro1-adamantanol seems to be the highest ever reported for an alcohol. A computational study of these species and their anions at both the MP2/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) levels was performed. Also studied were the tertiary alcohols (including their perfluorinated forms) derived from norbornane, bicyclo[2.2E2]octane and cubane. It was found that: (i) the intrinsic acidity of non-fluorinated bridgehead alcohols increases with the strain of the hydrocarbon framework and, (ii) perfluorination of these compounds strongly increases their acidity and, likely, significantly modifies their internal strain.

Herrero, Rebeca; Dávalos, Juan Z.; Abboud, José-Luis M.; Alkorta, I.; Koppel, I.; Koppel, I. A.; Sonoda, T.; Mishima, M.

2007-11-01

371

Optically based diagnostics for gas-phase laser development  

NASA Astrophysics Data System (ADS)

In this paper we describe several diagnostics that we have developed to assist the development of high power gas phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements of O2(a), small signal gain, iodine dissociation, and temperature. These are key operational parameters within COIL, and these diagnostics have been used world-wide to gain a better understanding of this laser system. Recently, we have developed and integrated a similar suite of diagnostics for scaling the EOIL system and will provide examples of current studies. We are also developing diagnostics for the emerging DPAL laser. These include monitors for small signal gain that will provide both a more fundamental understanding of the kinetics of DPAL and valuable data for advanced resonator design. We will stress the application of these diagnostics to realistic laser systems.

Rawlins, Wilson T.; Lee, Seonkyung; Galbally-Kinney, Kristin L.; Kessler, William J.; Hicks, Adam J.; Konen, Ian M.; Plumb, Emily P.; Davis, Steven J.

2010-09-01

372

Silicon nanowire-based devices for gas-phase sensing.  

PubMed

Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

Cao, Anping; Sudhölter, Ernst J R; de Smet, Louis C P M

2013-01-01

373

Tautomeric properties and gas-phase structure of acetylacetone.  

PubMed

The tautomeric and structural properties of acetylacetone, CH3C(O)CH2C(O)CH3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). The analysis of GED intensities resulted in the presence of 100(3)% of the enol tautomer at 300(5) K and 64(5)% of the enol at 671(7) K. The enol tautomer possesses Cs symmetry with a planar ring and strongly asymmetric hydrogen bond. The diketo form possesses C2 symmetry. The experimental geometric parameters of both tautomeric forms are reproduced very closely by B3LYP/aug-cc-pVTZ and MP2/cc-pVTZ methods. PMID:24758690

Belova, Natalya V; Oberhammer, Heinz; Trang, Nguen Hoang; Girichev, Georgiy V

2014-06-20

374

Conformational Study of Taurine in the Gas Phase  

NASA Astrophysics Data System (ADS)

The conformational preferences of the amino sulfonic acid taurine (NH2-CH2-CH2-SO3H) have been investigated in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) in the 6-14 GHz frequency range. One conformer has been observed, and its rotational, centrifugal distortion, and hyperfine quadrupole coupling constants have been determined from the analysis of its rotational spectrum. Comparison of the experimental constants with those calculated theoretically identifies the detected conformer unambiguously. The observed conformer of taurine is stabilized by an intramolecular hydrogen bond O-H···N between the hydrogen of the sulfonic acid group and the nitrogen atom of the amino group.

Cortijo, Vanessa; Sanz, M. Eugenia; López, Juan C.; Alonso, José L.

2009-08-01

375

The gas-phase thermochemistry of FeH  

NASA Astrophysics Data System (ADS)

The guided-ion-beam mass spectrometer apparatus and procedures described by Ervin and Armentrout (1985) and Sunderlin and Armentrout (1990) are used to investigate the gas-phase endothermic hydride-abstraction reactions of Fe(+) with propane, cyclopropane, n-butane, cyclopentane, and acetaldehyde as a function of ion translational energy. The results are presented in graphs and briefly characterized. Values determined (for temperature 298 K) include D0 Fe-H = 1.63 + or - 0.08 eV, D0 Fe(+)-H(-) = 8.77 + or - 0.08 eV, IE FeH = 7.37 + or - 0.10 eV, PA Fe(-) = 347.6 + or - 1.9 kcal/mol, and Delta(f)H FeH = 113.9 + or - 1.9 kcal/mol.

Schultz, Richard H.; Armentrout, P. B.

1991-02-01

376

Gas-phase generation and cyclisation reactions of imidoyl radicals.  

PubMed

Some 1,2-diarylimidoyl radicals were generated in the gas-phase by intramolecular radical translocation from ortho-imino-aryloxyl radicals, in turn generated under flash vacuum pyrolysis (FVP) conditions. The imidoyls reacted with XR ortho'-substituents in the N-aryl group to give (in most cases) modest yields of cyclisation products. Depending on the nature of the bridging atom (X), the formation of these products was initiated either by a further hydrogen atom translocation (X = CH(2)), or by ipso-attack onto the aryl group (R = Ph), or by direct substitution at the heteroatom (X = S). With XR = N(Me)Ph, the major reaction product was probably the result of a competing pathway not involving the corresponding imidoyl. PMID:22116614

Leardini, Rino; McNab, Hamish; Nanni, Daniele; Tenan, Anton G; Thomson, Andrew

2012-01-21

377

Correlated random-phase-approximation study of an anyon gas  

NASA Astrophysics Data System (ADS)

The correlated random-phase-approximation (CRPA) method is applied to study the ground-state and excited-state properties of an anyon gas. We perform a systematic 1/N expansion to the calculation of elementary excitations, where N is the statistical parameter. We find that the leading-(1/N)-order contributions are the same as those obtained by calculations of the RPA response functions. We then consider corrections to the RPA by a perturbation of the exchange interactions, and show that these higher-order corrections are important at large wave vectors. Our calculation gives an excitation spectrum in good agreement with that obtained by the exact solution of a small system.

Liu, B. H.; Wang, X. Q.; McLerran, L.

1991-06-01

378

Correlated random-phase-approximation study of an anyon gas  

SciTech Connect

The correlated random-phase-approximation (CRPA) method is applied to study the ground-state and excited-state properties of an anyon gas. We perform a systematic 1/{ital N} expansion to the calculation of elementary excitations, where {ital N} is the statistical parameter. We find that the leading-(1/{ital N})-order contributions are the same as those obtained by calculations of the RPA response functions. We then consider corrections to the RPA by a perturbation of the exchange interactions, and show that these higher-order corrections are important at large wave vectors. Our calculation gives an excitation spectrum in good agreement with that obtained by the exact solution of a small system.

Liu, B.H.; Wang, X.Q.; McLerran, L. (Theoretical Physics Institute, University of Minnesota, 116 Church Street S.E., Minneapolis, Minnesota 55455 (US))

1991-06-01

379

Reaction of atomic fluorine with silicon: The gas phase products  

SciTech Connect

SiF/sub 2/ and SiF/sub 4/ have been identified as gas phase products of the reaction between atomic fluorine and silicon. Atomic fluorine is supplied by a low density molecular beam hitting a silicon target in a high vacuum. Reaction products were detected by mass spectrometric measurements. Activation energies for the production of SiF/sub 2/ and SiF/sub 4/ were found to be 0.09 +- 0.02 and 0.15 +- 0.02 eV//sup 0/K, respectively, in good agreement with the values measured by flowing afterglow techniques. The reaction probability for the reaction 4F+Si..-->..SiF/sub 4/ was found to be 0.016 at 100 /sup 0/C.

Vasile, M.J.; Stevie, F.A.

1982-05-01

380

Uncertainties in gas-phase atmospheric iodine chemistry  

NASA Astrophysics Data System (ADS)

We present a comprehensive chemical mechanism for gas-phase iodine, to be used for modelling tropospheric chemistry. The mechanism has been compiled from evaluated data and individual literature studies, where available; a number of key processes have not been studied experimentally or theoretically and in these cases estimations have been made. The uncertainty associated with these assumptions is evaluated. We analyze the mechanism using a box-model under a variety of boundary layer scenarios - representative of environments where iodine species have been observed - to study the response of the chemical system to changes in the kinetic parameters of selected reactions. We focus in particular on key species such as IO, OIO, INO3 and I2Oy and the impact of iodine chemistry on ozone formation and HOx levels. The results indicate that the chemical system is most sensitive to reactions leading to comparatively stable iodine compounds, which should be a focus of future laboratory studies.

Sommariva, R.; Bloss, W. J.; von Glasow, R.

2012-09-01

381

Gas-phase SO 2 in absorption towards massive protostars  

NASA Astrophysics Data System (ADS)

We present the first detection of the nu3 ro-vibrational band of gas-phase SO2 in absorption in the mid-infrared spectral region around 7.3?m of a sample of deeply embedded massive protostars. Comparison with model spectra shows that the derived excitation temperatures correlate with previous C2H2 and HCN studies, indicating that the same warm gas component is probed. The SO2 column densities are similar along all lines of sight suggesting that the SO2 formation has saturated, but not destroyed, and the absolute abundances of SO2 are high ( ~ 10-7). Both the high temperature and the high abundance of the detected SO2 are not easily explained by standard hot core chemistry models. Likewise, indicators of shock induced chemistry are lacking. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.

Keane, J. V.; Boonman, A. M. S.; Tielens, A. G. G. M.; van Dishoeck, E. F.

2001-09-01

382

Gas phase hydrogen permeation in alpha titanium and carbon steels  

NASA Technical Reports Server (NTRS)

Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

Johnson, D. L.; Shah, K. K.; Reeves, B. H.; Gadgeel, V. L.

1980-01-01

383

Gas phase chromatography of halides of elements 104 and 105  

SciTech Connect

On-line isothermal gas phase chromatography was used to study halides of {sup 261}104 (T{sub {1/2}} = 65 s) and {sup 262,263}105 (T{sub {1/2}} = 34 s and 27 s) produced an atom-at-a time via the reactions {sup 248}Cm({sup 18}O, 5n) and {sup 249}Bk({sup 18}O, 5n, 4n), respectively. Using HBr and HCl gas as halogenating agents, we were able to produce volatile bromides and chlorides of the above mentioned elements and study their behavior compared to their lighter homologs in Groups 4 or 5 of the periodic table. Element 104 formed more volatile bromides than its homolog Hf. In contrast, element 105 bromides were found to be less volatile than the bromides of the group 5 elements Nb and Ta. Both 104 and Hf chlorides were observed to be more volatile than their respective bromides. 31 refs., 8 figs.

Tuerler, A.; Gregorich, K.E.; Czerwinski, K.R.; Hannink, N.J.; Henderson, R.A.; Hoffman, D.C.; Kacher, C.D.; Kadkhodayan, B.; Kreek, S.A.; Lee, D.M.; Leyba, J.D.; Nurmia, M.J. (Lawrence Berkeley Lab., CA (United States)); Gaeggeler, H.W.; Jost, D.T.; Kovacs, J.; Scherer, U.W.; Vermeulen, D.; Weber, A. (Paul Scherrer Inst. (PSI), Villigen (Switzerland)); Barth, H.; Gober, M.K.; Kratz, J.V. (Philipps-Univ., Marburg

1991-04-01

384

Estimation of gas phase mixing in packed beds  

SciTech Connect

An improved model is presented for estimation of the mixing of gaseous species in a packed bed for fuel conversion. In particular, this work clarifies the main characteristics of mixing of volatiles and oxidizers in a burning bed of high-volatile solid fuel. Expressions are introduced to represent the active role of degradation of the solid particles in the mixing within the gas phase. During drying and devolatilization the solids modify the behavior of the gas flow: the volatiles released from the surface of the particles increase the turbulence in the system, and hence the rates of the homogeneous reactions under mixing-limited conditions. Numerical experiments are carried out to test the validity of this conclusion regarding mixing in different geometries. The flow of volatiles leaving the fuel particles is shown to contribute significantly to mixing, especially at low air flows through a bed. However, the fraction of the particle surface where volatiles are released and its orientation in the bed should be better determined in order to increase the accuracy of the estimates of turbulent mixing. (author)

Frigerio, S. [CMIC Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan (Italy); Thunman, H.; Leckner, B.; Hermansson, S. [Department of Energy Conversion, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

2008-04-15

385

Atomic and molecular physics in the gas phase  

SciTech Connect

The spatial and temporal distributions of energy deposition by high-linear-energy-transfer radiation play an important role in the subsequent chemical and biological processes leading to radiation damage. Because the spatial structures of energy deposition events are of the same dimensions as molecular structures in the mammalian cell, direct measurements of energy deposition distributions appropriate to radiation biology are infeasible. This has led to the development of models of energy transport based on a knowledge of atomic and molecular interactions process that enable one to simulate energy transfer on an atomic scale. Such models require a detailed understanding of the interactions of ions and electrons with biologically relevant material. During the past 20 years there has been a great deal of progress in our understanding of these interactions; much of it coming from studies in the gas phase. These studies provide information on the systematics of interaction cross sections leading to a knowledge of the regions of energy deposition where molecular and phase effects are important and that guide developments in appropriate theory. In this report studies of the doubly differential cross sections, crucial to the development of stochastic energy deposition calculations and track structure simulation, will be reviewed. Areas of understanding are discussed and directions for future work addressed. Particular attention is given to experimental and theoretical findings that have changed the traditional view of secondary electron production for charged particle interactions with atomic and molecular targets.

Toburen, L.H.

1990-09-01

386

Gas-phase nuclear magnetic resonance studies of conformational kinetics  

NASA Astrophysics Data System (ADS)

The gas-phase conformational exchange kinetics of several amide and thioamide systems have been examined. The most fundamental amide system, formamide, has been studied extensively. The internal rotation rate constants for gaseous formamide are temperature and pressure dependent. The temperature dependent unimolecular high-pressure limit activation parameters are consistent with E? = 16.6(0.3) kcal mol-1 and A ? = 1.60(1.02) × 1013 sec-1 . The pressure dependent rate constants for formamide internal rotation are found to follow statistical RRKM kinetics. In addition, experimental and computational conformational analyses have been performed for solvated formamide systems. The internal rotation activation barriers are found to increase with increasing polarity of the solvent. The experimental values are compared to values calculated according to SC - IPCM and IPCM methodologies. The conformational exchange and equilibria in gas-phase asymmetrically substituted amides and thioamides have also been studied. The internal rotation activation barriers and conformational equilibria are found to be primarily influenced by the nature of the carbonyl substituent on the carbonyl or thiocarbonyl carbon in amides and thioamides. The conformational equilibria and activation energies are significantly different for the thioamides relative to their oxoamide analogs. Solvation significantly affects both the activation and conformational energies for all systems. The phase dependence of the values is attributed to solvent internal pressure effects and solvent stabilizing interactions. The Berry pseudorotation process in gaseous SF4 has been examined. Rate constants determined from exchange broadened 19F NMR spectra are temperature and pressure dependent. The temperature dependence of the unimolecular rate constants are consistent with E? = 11.9(0.2) kcal mol-1, A? = 3.56(1.09) × 1012 sec-1, ?G? = 12.2(0.2) kcal mol-1, ?H? = 11.3(0.4) kcal mol-1, and ?S? = -3.3(0.4) cal mol-1 K-1. The experimental values are compared to theoretical predictions using HF, MP2, DFT, MP4, and G2 methods. The pressure dependent rate constants agree well with RRKM predictions. Finally, the degenerate migration of the trimethylsilyl group in gaseous 5-trimethylsilylcyclopentadiene is studied. The temperature dependent rate constants for this process are consistent with ?G? = 15.7(0.1) kcal mol-1, ?H? = 15.4(0.2) kcal mol-1, and ?S? = -1.1(0.1) cal mol-1 K-1. The kinetic parameters are slightly higher than previously reported values for the neat liquid.

Taha, Angela Najah

387

Stages of homogeneous nucleation in solid isotopic helium mixtures.  

PubMed

We have made pressure and NMR measurements during the evolution of phase separation in solid helium isotopic mixtures. Our observations indicate clearly all three stages of the homogeneous nucleation-growth process: (1) creation of nucleation sites; (2) growth of the new-phase component at these nucleation sites; and (3) coarsening: the dissolution of subcritical droplets with the consequent further late-stage growth of the supercritical droplets. The time exponent for the coarsening, a=1/3, is consistent with the conserved order parameter Lifshitz-Slezov evaporation-condensation mechanism. PMID:18352566

Poole, M; Saunders, J; Cowan, B

2008-02-22

388

A model prediction of the yield of cloud condensation nuclei from coastal nucleation events  

NASA Astrophysics Data System (ADS)

The formation and evolution of new particles during coastal nucleation events are examined using the aerosol dynamic and gas-phase chemistry model AEROFOR2. Coastal regions are known to be a strong source of natural aerosol particles and are also strong sources of biogenic vapors which can condense onto aerosol particles, thus resulting in particle growth. A number of model simulations were performed to determine the instantaneous nucleation rate along with the source rate of a generic biogenic vapor leading to the observed particle size distributions which indicate the rapid appearance of ~105-106 cm-3 nucleation mode particles in this environment. Model calculations suggest values of 3 × 105 cm-3 s-1 to 3 × 106 cm-3 s-1 for the instantaneous nucleation rate and a value of 5 × 107 cm-3 s-1 for the condensable vapor source rate in order to reproduce the observed concentrations. A significant fraction of these new particles survive to grow into cloud condensation nuclei (CCN) sizes for supersaturations typically encountered in boundary layer clouds during subsequent evolution over 3 days under clear-sky conditions, thus contributing to the indirect radiative effect of aerosols. The amount of CCN is mainly affected by coagulation between particles and condensation of the biogenic vapor and, to a lesser extent, by condensation of sulphuric acid formed by DMS oxidation. In all simulated cases, an increase of more than 100% in CCN concentration, for supersaturations >0.35% was observed.

Pirjola, Liisa; O'Dowd, Colin D.; Kulmala, Markku

2002-08-01

389

Applying ion-molecule reactions to studies of gas-phase protein structure.  

National Technical Information Service (NTIS)

Whether solution phase differences in protein higher order structure persist in the gas phase, is examined by means of proton transfer reactions on ions generated by electrospray ionization of different solution conformations. Ion-molecule reactions were ...

R. R. Ogorzalek Loo J. A. Loo R. D. Smith

1992-01-01

390

Quantum Nucleation of Bubbles in Liquid Heliums  

NASA Astrophysics Data System (ADS)

As the temperature of liquid under negative pressure approaches the absolute zero, nucleation due to thermal fluctuations rarely occurs. Instead of thermal motion, quantum fluctuations may induce the formation of nuclei for transition into a new phase from the metastable state. In this study, a theoretical investigation with molecular cluster model was performed on liquid helium under negative pressure to examine the thermal as well as the quantum nucleation of bubbles and the cross-over temperature from the thermal to the quantum regime. The energy barrier against nucleation was estimated from the molecular interaction due to London’s dispersion force. The phase transition from liquid to vapor was shown to be only possible due to the quantum tunneling below 0.25 K for helium-4 and 0.175 K for helium-3. The cross-over temperatures which depends on the square root of the single particle quantum vibrational energy times the free energy of the critical cluster were comparable to the calculated results obtained through the density functional approach and the functional-integral approach. Also, the negative pressures needed for bubble nucleation on vortices lines were calculated and the results were found to be in good agreement with observations.

Kwak, Ho-Young; Jung, Jung-Yeul; Hong, Jae-Ho

2002-09-01

391

Power modulation control of a three-phase to single-phase matrix converter for a gas engine cogeneration system  

Microsoft Academic Search

Application of a three-phase to single-phase matrix converter for a 1 kW household gas engine cogeneration system is proposed. The matrix converter connects a three-phase permanent magnet synchronous generator of the cogeneration system to single-phase utility. Application of the matrix converter has the following advantages: (a) the generator efficiency will be improved because power factor control of the generator with

Y. Miura; S. Kokubo; D. Maekawa; S. Horie; T. Ise; T. Momose; Y. Sato

2008-01-01

392

Flow characteristics of gas–liquid two-phase flow in plate heat exchanger  

Microsoft Academic Search

In order to clarify the gas–liquid two-phase flow characteristics in a plate heat exchanger, gas–liquid two-phase flows in simulated heat exchangers with a single channel placed in a vertical plane were visualized by a neutron radiography method. Air–water adiabatic two-phase flows and chlorofluorocarbon R141b boiling two-phase flows were visualized, and two-dimensional void fraction distributions were measured from visualized images via

Hitoshi Asano; Nobuyuki Takenaka; Terushige Fujii

2004-01-01

393

Gas-Phase Reactions of Halogen Species of Atmospheric Importance.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) times 10 ^{-12}cm^{ -3}molecule^{-1}s ^{-1}. The reaction between I and NO_3 was found to occur at a rate of about 60% of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO_3 was found to be (4.5 +/- 1.9) times 10^{-10}cm^3 molecule^{-1}s ^{-1}. An upper limit for the heat of formation of IONO_2 of (21 +/- 3) kJmol^ {-1} was also derived. (Abstract shortened by UMI.).

Heard, Anne C.

394

Measurement of Gas-phase Acids in Diesel Exhaust  

NASA Astrophysics Data System (ADS)

Gas-phase acids were measured using chemical ionization mass spectrometry (CIMS) as part of the Diesel Engine Emission Research Experiment (DEERE). The CIMS technique, utilizing acetate ion (CH3COO-) as a reagent ion, proved to be a rapid (measurements on the order of seconds) and sensitive (several counts/pptv) method of quantifying the acid emissions. Diluted diesel exhaust measurements were made from a Constant Volume Sampling dilution tunnel using a light duty (1.9L turbocharged Volkswagen Jetta TDI) diesel engine equipped with an OEM diesel oxidation catalyst and exhaust gas recirculation, mounted on an engine dynamometer. Acids measured included isocyanic, nitrous, nitric, propionic and sum of lactic and oxalic, as well as other unidentified compounds. Complimentary measurements of CO, CO2, Total Hydrocarbon (THC), and NOx, were also performed. Several engine modes (different engine rpm and torque outputs) at steady state were examined to determine their effect on acid emissions. Emission rates with respect to NOx and fuel based emission factors were determined. Measurements of HONO fuel emission factors agree well with real-world measurements within a traffic tunnel.1 The first estimate of isocyanic acid emission factors from a diesel engine is reported, and suggests that the emission of this highly toxic compound in diesel exhaust should not be ignored. 1. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J.,Lorzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A.,and Platt, U.: Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel, Atmos. Environ., 35, 3385-3394, doi:10.1016/S1352-2310(01)00138-8, 2001.

Wentzell, J. J.; Liggio, J.; Li, S.; Vlasenko, A. L.; Staebler, R. M.; Brook, J.; Lu, G.; Poitras, M.; Chan, T.

2012-12-01

395

Nucleation in Synoptically Forced Cirrostratus  

NASA Technical Reports Server (NTRS)

Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

2004-01-01

396

Volumes of critical bubbles from the nucleation theorem.  

PubMed

A corollary of the nucleation theorem due to Kashchiev [Nucleation: Basic Theory with Applications (Butterworth-Heinemann, Oxford, 2000)] allows the volume V(*) of a critical bubble to be determined from nucleation rate measurements. The original derivation was limited to one-component, ideal gas bubbles with a vapor density much smaller than that of the ambient liquid. Here, an exact result is found for multicomponent, nonideal gas bubbles. Provided a weak density inequality holds, this result reduces to Kashchiev's simple form which thus has a much broader range of applicability than originally expected. Limited applications to droplets are also mentioned, and the utility of the p(T,x) form of the nucleation theorem as a sum rule is noted. PMID:16999490

Wilemski, Gerald

2006-09-21

397

Ion-Induced Nucleation from Sulfur Dioxide.  

NASA Astrophysics Data System (ADS)

Experiments were performed in a sealed circuit where the reactant gas or gases were introduced, in varying concentrations, into a purified carrier (air, N2, He, or Ar) of controlled humidity. Attempts to initiate nucleation were made by passing the gas through one of six different ion sources. These sources utilized one of three basic ionizing mechanisms: (alpha)-particle bombardment from a radioactive source, corona discharge, and evaporation from a charged spray. The ions introduced into the reacting system in different experiments were in some cases bipolar, and in other cases unipolar of either sign. Secondary radicals could be avoided with certain sources or introduced separately. The majority of the experiments dealt with only SO(,2) and H(,2)O but a few included NH(,3) as well (Appendix A). The rate of nucleation (number of particles created per unit volume, per unit time) was determined with a condensation nucleus counter. Nucleation curves (rate versus SO(,2) concentration) obtained with the corona and radioactive sources, showed saturation with respect to SO(,2) concentration by 30 ppm. The maximum rates obtained depended upon the concentration of ions and of water vapour, but were independent of the amount of O(,2). Both positive and negative ions were found to be efficient agents for evoking nucleation, with only minor differences in nucleation level being evident. Water -derived radicals were found to be active, when using argon carrier, but at a much lower efficiency level than the ions. Spray ions did not induce nucleation. Aerosol particles were tested for electrical charge and found to be neutral. Sizes were estimated with diffusion batteries (Appendix B). A mass spectrometric study of the ions was performed. It was concluded that energetic ions are effective in inducing oxidation reactions leading to SO(,3) and that this subsequently nucleates with water vapour. The main oxidation sequence probably does not involve O, OH or species derived from it and it is suggested that activation of SO(,2) followed by reaction with another SO(,2) molecule constitutes the principal pathway.

Diamond, Gerald Leo

398

School Heating - Gas vs. Electric. Phase 1A - Effect on Construction Costs, (Updating Phase 1 Report Dated January 1965).  

ERIC Educational Resources Information Center

Phase 1A updates the original study of January 1965 and contains the sevenmost recent schools which in their development stages were bid for both gas and electric heating systems. In all cases the bids were for first cost, not for ultimate operating expense. Although the differences were relatively minor, six out of the seven gas bids were lower…

Valvoda, Frank R.

399

Gas Phase Conformations of Tetrapeptide Glycine-Phenylalanine-Glycine-Glycine  

NASA Astrophysics Data System (ADS)

Systematic search of the potential energy surface of tetrapeptide glycine-phenylalanine-glycine-glycine (GFGG) in gas phase is conducted by a combination of PM3, HF and BHandHLYP methods. The conformational search method is described in detail. The relative electronic energies, zero point vibrational energies, dipole moments, rotational constants, vertical ionization energies and the temperature dependent conformational distributions for a number of important conformers are obtained. The structural characteristics of these conformers are analyzed and it is found that the entropic effect is a dominating factor in determining the relative stabilities of the conformers. The measurements of dipole moments and some characteristic IR mode are shown to be effective approaches to verify the theoretical prediction. The structures of the low energy GFGG conformers are also analyzed in their connection with the secondary structures of proteins. Similarity between the local structures of low energy GFGG conformers and the ?-helix is discussed and many ?- and ?-turn local structures in GFGG conformers are found.

Chen, Hui-bin; Wang, Yao; Chen, Xin; Lin, Zi-jing

2012-02-01

400

Directed gas-phase formation of the ethynylsulfidoboron molecule.  

PubMed

As a member of the organo sulfidoboron (RBS) family, the hitherto elusive ethynylsulfidoboron molecule (HCCBS) has been formed via the bimolecular reaction of the boron monosulfide radical (BS) with acetylene (C2H2) under single collision conditions in the gas phase, exploiting the crossed molecular beams technique. The reaction mechanism follows indirect dynamics via a barrierless addition of the boron monosulfide radical with its boron atom to the carbon atom of the acetylene molecule, leading to the trans-HCCHBS intermediate. As predicted by ab initio electronic structure calculations, the initial collision complex either isomerizes to its cis-form or undergoes a hydrogen atom migration to form H2CCBS. The cis-HCCHBS intermediate either isomerizes via hydrogen atom shift from the carbon to the boron atom, leading to the HCCBHS isomer, or decomposes to ethynylsulfidoboron (HCCBS). Both H2CCBS and HCCBHS intermediates were predicted to fragment to ethynylsulfidoboron via atomic hydrogen losses. Statistical (RRKM) calculations report yields to form the ethynylsulfidoboron molecule from cis-HCCHBS, H2CCBS, and HCCBHS to be 21%, 7%, and 72%, respectively, under current experimental conditions. Our findings open up an unconventional path to access the previously obscure class of organo sulfidoboron molecules, which are difficult to access through "classical" formation. PMID:24842647

Yang, Tao; Parker, Dorian S N; Dangi, Beni B; Kaiser, Ralf I; Stranges, Domenico; Su, Yuan-Hsiang; Chen, Si-Ying; Chang, Agnes H H; Mebel, Alexander M

2014-06-11

401

Surface plasmon sensing of gas phase contaminants using optical fiber.  

SciTech Connect

Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H{sub 2}, H{sub 2}S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 70mTorr partial pressures of H{sub 2} using this technique and <280 {micro}Torr partial pressures of H{sub 2}S. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H{sub 2}, H{sub 2}S, and H{sub 2}O without changing the fiber or the analytical system.

Thornberg, Steven Michael; White, Michael I.; Rumpf, Arthur Norman; Pfeifer, Kent Bryant

2009-10-01

402

Gas phase chemistry of dinitramide and nitroacetylide ions  

NASA Astrophysics Data System (ADS)

Using the tandem flowing afterglow-selected-ion flow tube, we have examined the basicity, reactivity, electron binding energy and collision-induced dissociation of two novel nitro species, the dinitramide ion (N(NO2)-2) and the nitroacetylide ion (O2NC[triple bond; length as m-dash]C-). Dinitraminic acid is among the strongest known gas phase acids with [Delta]H°acid [less-than-or-equals, slant] 310 kcal mol-1. The conjugate base, dinitramide anion, has a high electron binding energy, is extremely unreactive and is a very poor nucleophile. Collision-induced dissociation of dinitramide anion generates the O2N=N- anion. Nitroacetylene is a moderately strong acid with [Delta]H°acid = 354 ± 4 kcal mol-1; this value is similar to those of other nitro compounds and substituted acetylenes. The nitroacetylide ion is generally unreactive but exhibits a rich chemistry upon reaction with hydrogen sulfide. The anion has a high electron binding energy and generates four ions upon collision-induced dissociation, ONC-, C-2, C2O-, and CN-.

Schmitt, Robert J.; Krempp, Michele; Bierbaum, Veronica M.

1992-09-01

403

Fullerene-impregnated ionic liquid stationary phases for gas chromatography.  

PubMed

A new method has been developed to facilitate the use of fullerenes as stationary phases (SPs) in gas chromatography (GC). In this method, ionic liquids (ILs) are used as solvents to coat fullerenes (C(60), amino-C(60) and hydroxy-C(60)) onto GC columns. However, the ILs serve not just as coating solvents but also act synergistically with fullerenes to provide unique properties as stationary phases, namely dual modal characteristics. They act as non-polar SPs when separating non-polar analytes (aromatic hydrocarbon mixtures and alkane mixtures), and as polar SPs for polar analytes (e.g., alcohol mixtures). The polarity of the stationary phase can be adjusted by changing either the type of the IL and/or by adding either C(60) (or its amino or hydroxy derivatives) to the IL. It was found that C(60) and its derivatives produce not only a change in the polarity of the SP but also substantial enhancement in separation efficiencies for both non-polar and polar analytes. More importantly, when added to the IL SP, C(60) improves separation efficiencies not just for non-polar analytes (aromatic hydrocarbon mixtures and alkane mixtures) but also for polar analytes (mixtures of ortho-, meta- and para-xylene and alcohol mixtures) as well. Moreover, C(60) SP provides higher efficiencies than amino-C(60) and hydroxy-C(60) for separation of polar analytes. This is rather surprising considering that not only are amino-C(60) and hydroxy-C(60) more polar than C(60), but that the IL used to coat the amino- and hydroxy-C(60) (i.e., N-ethylpyridinium trifluoroacetate, [EtPy(+) CF(3)COO(-)]) is more polar than the IL used to coat the C(60) (i.e., octylmethylimidazolium bis(trifluoromethyl)sulfonyl)amide], [OMIm(+) (CF(3)SO(2))(2)N(-)]). Moreover, compared to its amino and hydroxy derivatives, the concentration of C(60) in the column was 10 times lower. PMID:18365114

Tran, Chieu D; Challa, Santhosh

2008-04-01

404

On the ice nucleation spectrum  

NASA Astrophysics Data System (ADS)

This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.

Barahona, D.

2012-04-01

405

Statistical analysis of the phase holdup characteristics of a gas-liquid-solid fluidized bed  

Microsoft Academic Search

Experiments have been carried out to study the individual phase holdup characteristics in a cocurrent three-phase fluidized bed. An antenna type modified air sparger has been used in the gas-liquid distributor section, for uniform mixing of the fluids with the gas moving as fine bubbles to the fluidizing section. This arrangement also reduces the pressure drop encountered through a conventional

H. M. Jena; B. K. Sahoo; G. K. Roy; B. C. Meikap

2009-01-01

406

Research in Korea on Gas Phase Synthesis and Control of Nanoparticles  

Microsoft Academic Search

Research activity into the gas phase synthesis of nanoparticles has witnessed rapid growth on a worldwide basis, which is also reflected by Korean research efforts. Nanoparticle research is inherently a multi-disciplinary activity involving both science and engineering. In this paper, the recent studies undertaken in Korea on the gas phase synthesis and control of nanoparticles are reviewed. Studies on the

Mansoo Choi

2001-01-01

407

DETERMINATION OF GAS-PHASE DIMETHYL SULFATE AND MONOMETHYL HYDROGEN SULFATE  

EPA Science Inventory

Analytical techniques have been developed for the collection and determination of gas phase dimethyl sulfate and monomethyl sulfuric acid in the flue lines and plumes of power plants and in the ambient atmosphere. The techniques involve the collection of the gas phase species in ...

408

Gas-Phase Deposition of Polychlorinated Biphenyls (PCBs) to a Water Surface Sampler  

Microsoft Academic Search

In this study a water surface sampler (WSS) was utilized to directly measure gas phase deposition of polychlorinated biphenyls (PCBs). The measured gas phase PCB fluxes averaged about 880 ± 660 ngmd, which was higher than the fluxes calculated using simultaneously measured air and water concentrations for natural surface waters. These large fluxes were due to fact that the measured

YÜCEL TASDEMIR; THOMAS M. HOLSEN

2006-01-01

409

Calculation of CO 2 gas phase diffusion in leaves and its relation to stomatal resistance  

Microsoft Academic Search

A new theory and experimental method was developed to measure the diffusion resistance to CO2 in the gas phase of mesophyll leaf tissue. Excised leaves were placed in a chamber and their net evaporation and CO2 assimilation rates measured at two different ambient pressures. These data were used to calculate CO2 gas phase diffusion resistances. A variety of field grown

J. W. Cary

1981-01-01

410

WHERE ARE THE LIMITS OF THE GAS-PHASE FLUORESCENCE ON THE POLYCYCLIC AROMATIC COMPOUND ANALYSIS?  

Microsoft Academic Search

The aim of this work has been centered on the development of a detection system which could be useful to determine polycyclic aromatic hydrocarbon (PAH) emissions in power generation processes where PAHs are released to the atmosphere in the gas phase. In this way, a suitable sensor based on gas phase fluorescence spectroscopy was designed to facilitate the PAH analysis,

A. M. Mastral; T. García; J. M. López; R. Murillo; M. S. Callén; M. V. Navarro

2004-01-01

411

OMVPE growth and gas-phase reactions of AlGaN for UV emitters.  

National Technical Information Service (NTIS)

Gas-phase parasitic reactions among TMG, TMA, and NH3, are investigated by monitoring of the growth rate/incorporation efficiency of GaN and AlN using an in-situ optical reflectometer. It is suggested that gas phase adduct (TMA: NH(sub 3)) reactions not o...

J. Han J. J. Figiel M. H. Crawford M. A. Banas M. E. Bartram

1998-01-01

412

Importance of the gas phase role to the prediction of energetic material behavior: An experimental study  

SciTech Connect

Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6 mm{+-}0.4 mm exists below which ignition by CO{sub 2} laser is not possible at the tested irradiances of 29 W/cm{sup 2} and 38 W/cm{sup 2} for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

Ali, A.N.; Son, S.F.; Asay, B.W.; Sander, R.K. [Los Alamos National Laboratory, MS C920, Los Alamos, New Mexico 87544 (United States)

2005-03-15

413

Phase-field modeling of gas bubbles and thermal conductivity evolution in nuclear fuels  

Microsoft Academic Search

A phase-field model was developed to simulate the accumulation and transport of fission products and the evolution of gas bubble microstructures in nuclear fuels. The model takes into account the generation of gas atoms and vacancies, and the elastic interaction between diffusive species and defects as well as the inhomogeneity of elasticity and diffusivity. The simulations show that gas bubble

Shenyang Y. Hu; Charles H. Henager Jr.; Howard L. Heinisch; Marius Stan; Michael I. Baskes; Steven M. Valone

2009-01-01

414

NAT nucleation and denitrification in the polar stratosphere  

NASA Astrophysics Data System (ADS)

Nitric acid trihydrate (NAT) particles in the polar stratosphere are known to influence the chemistry of ozone depletion. NAT particles, along with other liquid and crystalline particles, provide heterogeneous surfaces for chlorine activation. More importantly, they can take up significant amounts of HNO3 from the gas phase and transport HNO3 downward by sedimentation. This can lead to denitrification, in the Arctic typically at altitudes above about 20 km, and a re-nitrification below, at the level where the NAT particles evaporate. The nucleation rate of NAT particles is a critical parameter for the simulation of this process. Very low NAT nucleation rates around 2?10-9cm-3s-1 have been deduced for low NAT supersaturations from observations. In previous studies, vertical HNO3 transport has been successfully simulated by Lagrangian 3-D simulations using a constant NAT nucleation rate of around 2?10-9cm-3s-1, for the Arctic winters in the years 2003 and 2005. However, for winter 2009/2010, this approach does not generate satisfying results. Here, saturation dependent NAT nucleation rates were derived from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), observations under the assumption that NAT nucleates heterogeneously on dust particles that are characterized by active sites with a certain occurrence probability distribution depending on the contact angle. Simulations with the Zurich Optical and Microphysical box Model (ZOMM) along back-trajectories starting from points where PSCs were observed by CALIPSO allow the parametrisation of heterogeneous nucleation rates for NAT and ice on dust, and the reproduction of the different PSC classes observed. We present simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS) of the winter 2009/2010 applying this new parametrisation of heterogeneous NAT nucleation rates. The CLaMS simulation is initialized using a combination of MLS, MIPAS-ENVISAT and ACE-FTS data. The simulation shows good agreement of chemical trace species with observations, especially H2O and HNO3, which are important for the reliable simulation of HNO3 supersaturations over NAT. This is shown by comparisons with in-situ CFH frost point hygrometer sondes and satellite based observations of H2O and HNO3 by MIPAS-ENVISAT, MLS, and ACE-FTS. Comparisons of the size distribution of the simulated NAT particles with the observations by a Forward Scattering Spectrometer Probe (FSSP) aboard the high-flying research aircraft Geophysica operated in the winter 2009/2010 indicate good agreement, even though the largest observed particles are not reproduced by the simulation. The simulation also reproduces the HNO3 redistribution in the Arctic winter 2009/2010 with denitrification and the re-nitrification peaks as observed by the ACE-FTS satellite instrument and in-situ observations by the SIOUX instrument operated aboard Geophysica.

Grooß, Jens-Uwe; Engel, Ines; Hoyle, Christopher R.; Luo, Beiping; Peter, Thomas; Frey, Wiebke; Molleker, Sergej; Borrmann, Stephan; Schlager, Hans; Vömel, Holger; Kivi, Rigel; Walker, Kaley A.; Santee, Michelle L.; Stiller, Gabriele; Pitts, Michael; Müller, Rolf

2013-04-01

415

Crystallization and nucleation kinetics in volcanic systems  

NASA Astrophysics Data System (ADS)

The main objective of this experimental study is to constrain and quantitatively model the complex solidification process that transforms a magma in a solid material. Of major interest are crystal nucleation and growth driven by isothermal decompression of hydrous magmas, and comparison with results from more abundant crystal growth/nucleation data obtained in isobaric cooling experiments. This research concerns two different volcanic systems, Pantelleria (peralkaline rhyolite) and Stromboli (basalt), to better understand how crystallization kinetics can affect different magma compositions. For Stromboli volcanic system TZM apparatus has been used to perform decompression runs at Bayerisches Geoinstitut in Bayreuth (DE). As for Pantelleria composition, cooling experiments has been done using IHPV devices at ISTO of Orléans (FR), on the basis of previous phase equilibrium work (Di Carlo et al., 2010). First obtained results for Stromboli case show high rates of nucleation and crystal growth during the initial stages of crystallization which were followed by crystal growth at approximately constant number densities as equilibrium was approached. Shapes of crystals growing in melts are controlled by the kinetics of crystallization and may provide information about the degree of undercooling experienced by batches of magma en route to the surface (Lofgren, 1980). The study of crystallization kinetics through phases growth rates (Couch et al., 2003), together with the calculation of nucleation density and nucleation rates (Hammer et al., 1999) represent a step toward the estimation of the time scales of magmatic processes in volcanic systems and the interpretation of shallow magmatic processes. The results for Stromboli suggest average crystal growth timescales on the order of weeks, but this is complicated by clear evidence that some crystals have experienced repeated periods of both dissolution and growth (Landi et al., 2004).

Agostini, C.; Fortunati, A.; Carroll, M. R.; Scaillet, B.; Landi, P.

2011-12-01

416

Sampling and determination of gas-phase hydrogen peroxide following removal of ozone by gas-phase reaction with nitric oxide  

SciTech Connect

A method for determination of hydrogen peroxide in the ambient atmosphere is described, using impinger or diffusion scrubber collection of hydrogen peroxide with aqueous-phase analysis by an enzyme-catalyzed fluorescence technique. Interference from ozone at ambient levels is removed by gas-phase titration with excess nitric oxide. The impinger and diffusion scrubber collection techniques are shown to give equivalent results for atmospheric gas-phase hydrogen peroxide with limits of detection of 0.1 ppbv for approximately 60-min and 10-min sampling times, respectively.

Tanner, R.L.; Markovits, G.Y.; Ferreri, E.M.; Kelly, T.J.

1986-01-01

417

Systems and tanks therefor for storing products in the liquid phase that are normally in the gas phase  

Microsoft Academic Search

A system is described for storing in the liquid phase a product that is entirely in the gas phase under atmospheric pressure and ambient temperature conditions. It includes an upstanding storage tank that is hermetically sealed and is heat-insulated on the bottom wall and side wall, an upstanding tube in the center of the tank guiding a floating roof that

Mair

1970-01-01

418

Microfabricated gas chromatograph for rapid, trace-level determinations of gas-phase explosive marker compounds.  

PubMed

A prototype microfabricated gas chromatograph (?GC) adapted specifically for the rapid determination of selected gas-phase marker compounds of the explosive 2,4,6-trinitrotoluene (TNT) at sub-parts-per-billion (

Collin, William R; Serrano, Gustavo; Wright, Lindsay K; Chang, Hungwei; Nuñovero, Nicolás; Zellers, Edward T

2014-01-01

419

Amyloid fibril networks nucleated under oscillatory shear  

NASA Astrophysics Data System (ADS)

The process of amyloid fibril formation is of interest due to the link between these self-aggregating proteins and the progression of neurodegenerative disease. More recently, research has been directed at the exploitation of self-assembly properties of amyloid proteins for use as templates for nanowires and fibrillar networks. Insulin is an ideal protein for these purposes due to the ease of aggregation, as well as the large aspect ratio and high chemical stability of the produced fibrils. Insulin in pH 2 solution quickly forms aggregates in the presence of 65 ^oC heat. We have investigated the effect of oscillatory shear on the nucleation and growth of amyloid fibrillar networks using rheology and TEM to characterize the mechanical properties and structure of the network respectively. We contrast networks nucleated under oscillatory shear with networks nucleated in static and agitated conditions, and discuss network properties in the context of use in templating nanostructures. We find that the structural characteristics of the formed networks, including the density of fibrils, are affected by shear during the nucleation phase of amyloid growth.

Batzli, Kiersten; Love, Brian

2013-03-01

420

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process.  

PubMed

The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism. PMID:15296221

Nikolaev, Pavel

2004-04-01

421

Source apportionment of wintertime gas-phase and particle-phase air pollutants using organic compounds as tracers  

Microsoft Academic Search

Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contribution to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbon and particle-phase

James J. Schauer; Glen R. Cass

2000-01-01

422

Design and Development of Gas-Liquid Cylindrical Cyclone Compact Separators for Three-Phase Flow  

Microsoft Academic Search

The objective of this five-year project (October 1997 - September 2002) was to expand the current research activities of Tulsa University Separation Technology Projects (TUSTP) to multiphase oil\\/water\\/gas separation. This project was executed in two phases. Phase I (1997 - 2000) focused on the investigations of the complex multiphase hydrodynamic flow behavior in a three-phase Gas-Liquid Cylindrical Cyclone (GLCC) Separator.

R. S. Mohan; O. Shoham

2001-01-01